Wednesday, October 29, 2014

Mysterious piles of silvery grains in the desert

I like my social media connections very much, even if I do spend much too much time with them. On Facebook, BugGuide and Flickr I am connected to many knowledgeable experts in their fields and creative artists whose work I would otherwise never get to see.
I bring in my own contributions by helping local friends to solve their bug mysteries and identify the occasional lizard or bird.
A couple of weeks ago, I ran into a mysterious 'thing' myself. Actually, I found 'it' by kicking over a long dried cow pie, left in the state land behind our property by cattle that was moved out years ago. But I still find the occasional bug or banded gecko hiding in those places ...

This time the ground under several pies was covered with a grainy silver gray substance. The grains were very regular in size. In my macro photos they also appeared sculpted or textured. There were tiny silver fish running between them.

Silver fish eggs? No, every female lays up to 100 in her live time. It would have taken a village or a small town of silver fish to produce this many.

I put the image on Facebook rather than BugGuide because I wasn't sure that this had anything to do with insects.
Rich Hoyer immediately suggested seeds.

After the monsoon the desert was covered in a golden blanket of chinch weed. It's still blooming.   Many plants are already setting their papus-equipped fruit.

There would have been enough chinch weed seeds to collect, but those seeds are long and dark. After knowing what to look for I actually found about three of them among thousands of the shorter ones. There is one in the bottom right corner.

So what are the little grey seeds? James Trager suggested mint or euphorbia. After searching for a long time I came up with one plant that is probably in the mint family, but it is by far too uncommon.
Euphorbia then?

 I sent the photo to Tom VanDevender who has a seed collection for the Sky Island Alliance. I had even discovered a seed pod in one of my photos by now. Yes, they are euphorbia seeds and can the alliance please keep the nice photo for their files? Sure.

 But now I wanted to know the exact species. There are patches of a small brownish green, prostrate weed all over, but I had completely ignored it because it is so unremarkable and common. Does it even flower? Of course. I just needed a magnifying glass to see flowers and even little seedpods.

Probably Chamaesyce/Euphorbia micromera
 Actually, I soon recognized that there were two species around and posted photos of both on FB.  FB friend Burr Williams from Texas then linked my query to the young botanist Nathan Taylor who actually specializes in 'prostrate euphorbia species' and who was glad and excited to help!

Chamaesyce/Euphorbia abramsiana
 He not only identified the two spp from our state land but also a third that had been in my files because of a bee fly that uses its tiny flowers.

Euphorbia/Chamaesyce albomarginata with Hemipenthes lepidota Cochise Co. AZ
So now think we know that the grainy stuff is indeed Euphorbia seeds, but how did it get under the old cow pie? Many FB friends speculated. The idea that the cow fed on the plant and then somehow segregated the seeds to expel them in a dense layer seemed unlikely. Also the seeds were fresh and the cow gone for years. It also wasn't wind drift that had piled up, because the cow pie was still sticking to the ground before I kicked it.

Of course, any collection of small seeds suggests ants. Many plants actually equip each seed with a little treat called elaiosome,, so ants will carry the seeds to their nests, eat the treat and throw out the seed, still intact (Seed dispersal by ants (myrmecochory).
Our two great collectors in the area are Veromessor pergandei and  Pogonomyrmex rugosus. But none of them seemed to be around in the vicinity of the cow dung. Also, both species tend to bring their harvest to their nests rather the storing it somewhere else.  

Under many dry cow pies, there are colonies of Solenopsis xyloni (Southern Fire Ant) a little ant that I only knew as a fierce predator. But James Trager told me that they also collect seeds. So I went through my pictures again. Yes! There are the little guys working among the seeds, and there even seems to be an entrance to a deeper more subterranean part of their nest on the left side. Remember that the entire seed pile was originally under ground, or at least under a very old piece of cow dung.

There, mystery solved! Net working and discussing worked. Except: what are those amber colored seeds? we thought that they were gray ones that had lost a waxy outer coating. looking more closely, I do not think so anymore. So? Suggestions?

Wednesday, October 22, 2014

Aposematic caterpillars from poisonous host plants

Yesterday I found some caterpillars on the shoulder of Catalina Highway, just above Molino Basin.

Pipevine Swallowtail (Battus philenor)  feeding on Southwestern Pipevine (Aristolochia watsonii)
 Caterpillars of the Pipevine Swallowtail (Battus philenor)  feed on Aristolochia watsonii (Watson's Dutchman's pipe, southwestern pipevine, Indian root, snakeroot) which seems to be their only wild food plant around here.

Southwestern Pipevine (Aristolochia watsonii) flower
 Aristolochia watsonii is  rather poisonous, Aristolochic acid being the main toxin. That's  nasty stuff, even though it is has had medicinal uses in ancient Egypt, Greece and Rome and is still used in traditional Chinese medicine. It's names Birthwort and Snakeweed point at some its uses. In modern western medicine it is recognized as carcinogenic. It can cause mutations and  kidney failior.

Nevertheless, Pipevine Swallowtail caterpillars feed exclusively on plants in the genus Aristolochia. Besides occurring on our endemic vine they can also be found on a tropical relative that is cultivated at Tohono Chul Park.

The caterpillars themselves are not negatively impacted by the toxin. Their physiology is adapted to dealing with it. They sequester the toxin in their bodies and become poisonous and probably bad tasting themselves. Their aposematic colors, either red with lighter red appendages or black with red spikes (the occurrence of either morph seems to be temperature dependent)  warns predators not to bother them. For a warning like this to be effective, the toxin should be unpleasant but not deadly so an inexperienced predator has a chance to learn by trial, the predator should be able to see colors and he needs to be smart enough to learn. This probably all applies to birds and reptiles and maybe small rodents like the grasshopper mouse..

caterpillar with partly extended osmeterium (topright end)
Some  predators do not have the sense to understand (or see) the warning color and threaten the caterpillar anyway,  At close contact, the caterpillar will then stick out a fleshy, forked structure from its prothorax. This organ, the osmeterium, is common to caterpillars of all Swallowtail species. It  emits a foul smelling secretion containing terpens that should warn off even a color-blind attacker.

Mating Pipevine Swallowtails. Note that the female has only just emerged from the chrysalis that can be seen in the left bottom corner
Even after metamorphosis, Pipevine Swallowtail adults still retain the chemical protection acquired by the caterpillar. It makes them so untouchable that another Butterfly, the Red-spotted Purple, Limenitis arthemis, mimics the looks of a female Pipevine Swallowtail very convincingly. The Purple' caterpillar feeds on Prunus sp. and trees in the Willow family and is probably quite edible. Incidentally, Red-spotted Purple and White Admiral are two races of the sames species of brush-footed Butterflies. Only the Purple shares the distribution of the Pipevine and also its looks. The White Admiral with his broad white band on black ground does not at all resemble the Pipevine. 

Red-spotted Purple Limenitis arthemis catterpillar and adults


Tuesday, October 21, 2014

A walk in the Rock-disk Park

Here are just some early autumn photos from an area in Marana, Arizona, that was flooded by the Santa Cruz River during the recent storm. This is a very temporary wetland: I was completely dry for over a year. It is used as a golf-disk park.(Frisbee).  But now the river has changed its bed and keeps flowing into the low laying basin.

Waterbirds and birds that depend on aquatic-breeding insects like gnats had found the new lake already. Vermillion Flycatchers and Black Phoebes were hunting from the branches of submersed trees.  The air was alive with swallows and I was surprised to hear and see a number of Kingfishers, so fish must have been washed in from the river. Squeaking their characteristic protest, several bullfrogs leaped from under my feet. So there is plenty of food for the 3 species herons and egrets that I saw during my short visit.

Just before sunset, thousands of Yellow-headed Blackbirds traveled along the river and descended into the lush vegetation to roost overnight. Tomorrow morning they will take off to feed in agricultural fields in Avra Valley and the Santa Cruz Flats.

Skimmer exuvia were clinging to weeds at the water's edge. Maybe they got started in a quiet part of the river before the flood. Adult 'Odes' are everywhere now. The dominant species by far is the Mexican Amberwing

Sharp-leafed Ground Cherry, Douglas Nightshade, Datura, Desert Tobacco, Buffalo Bur, Silver-leafed Nightshade, Tree Tobacco: All in the Nightshade family
 Most of the water comes from several treatment plant downstream. The municipalities in charge recently improved the water treatment facilities so the water quality should improve. But so far the effluent was extremely nitrogen rich. That is reflected in the vegetation: I have counted at least 7 different species of nitrogen loving nightshades, all in extraordinarily huge specimens.

Proboscidea parvivlora, Devil's Claw, flower, fruit and Manduca sexta caterpillar (Tomato Hornworm)
Nightshades produce potent chemical components. Some, like nicotine, have evolved as defenses against herbivores, others, like the tropane alkaloids of Datura may also lure pollinators. Several species of insects coevolved to use night shades as hosts, some of them doubtlessly sequestering the toxins for their own protection.

Unusually dark Manduca rustica caterpillar on Desert Willow, and a green specimen from our backyard for comparison
The county gardeners planted desert trees like Velvet Mesquite and Desert Willow along the paths of the park, but they seem to be hopelessly out-competed by the established population of Mexican Palo Verde and the invasive Tamarisk, probably due to the high nitrogen content of the soil.

Those well irrigated trees are always full of wasps and American Snout Butterflies even though they are not blooming. They seem to either exude juices or host aphids (that I cannot find) that produce a lot of honey dew. This time there were all major development stages of Cactus Ladybugs on one tamarisk twig.

As I was searching the ground for grasshoppers suddenly some dry little sticks began to glitter in the last rays of the setting sun: Male sweat bees, Dieunomia nevadensis arizonensis were settling in to spend the night. After they settled they began to thoroughly preen (video here).

Sphaenothecus bivittata (left) and Crossidius suturalis intermedius (right)
The last blooming Rabbit Bushes  (Haplopappus or Isocoma sp.) still hosted a variety of beetles. The sturdy Crossidium suturalis breeds in the stems of the small yellow composite.  The little Sphaenothecus breeds in Mesquite and Roses.Beetles of the Ripiphorus sp. below send their larvae home with ground-nesting, solitary bees to be raised as brood parasites. Hard to believe that he even is a beetle. But that's another story story - here


Thursday, October 9, 2014

I learned something new in a round-about way

I just learned something that I had missed so far because I was always too squeamish to observe it. The birth of a maggot that is. I remember being fascinated by a wiggling masses of white worms on a dead mouse that a hawk had dropped in our backyard - I was 4 and we had just moved from the city to the countryside. My mother was properly repulsed and worried about germs. I had also gotten a whiff of a smell that was more than unpleasant. So - no forensic interest was triggered in early childhood or even later when studying physiology and having to breed flies for their big eyes that were easy targets for beginning neurophydiologists' electrodes.

Entomologist collecting beetles from an old cow carcass
Nowadays I sometimes carefully look over the shoulder of an entomologists who sees animal cadavers as an interesting source for beetle specimens, but even then we tend to stay away from the most smelly rotting stages that flies prefer.

Stapelia gigantea
However, living in the desert, I love succulents, including Stapelia species from Africa. These plants use a very deceptive strategy to attract pollinators: instead of offering nectar or an abundance of pollen and the sweet fragrances that would announce those delicacies, Stapelias stink. They imitate very convincingly the odor of putrefaction, the odor of rotting meat. The one on our patio, Stapelia gigantea, the Giant Starfish Cadaver Flower, also looks like a piece of wrinkled, ripped skin with remnants of fur still on it.  All that of course to attract their pollinators. According to Wikipedia those would be mostly Blow Flies in the family Calliphoridae. Those green bottle flies would crawl around among anthers and stigma trying to find a good location to deposit their eggs on the presumed rotting meat and in the process pollinate the flowers.

Powerpoint file about deception directed at pollinators, examples Ophris and Stapelia
I sometimes give talks about pollination by insects other than honey bees, so when flowers of my  patio plant had opened up and some insects approached its center I was ready with my camera.
But at first, there were no green bottle flies.

Braconidae (Braconid Wasps), Alysiinae
 The first visitors I recognized as parasitic wasps. I had seen them before. Whenever I find a dead mouse in the garage or a bird that had hit a window pane these black and red wasps are around. They are associated with Sarcophagids, the big grey Flesh Flies whose larvae they use as hosts for their own offspring. 

2 wasps, and a Flesh Fly
Another smaller wasp and a big Sarcophaga sp. female arrived next. I knew that the fly was a female because her big compound eyes did not touch on top of her head as the male's eyes do (that much I do remember from my electrophysiology days). 

Sarcophage female giving birth to live maggots
 For me, the interesting part began here:
She crawled around in the center of the flower, probably doing the pollination duty that she was tricked into. Then she emitted bursts of sharp buzzing. At this time her abdomen was pointed pretty much at the center of the flower, the area that probably emits the foul smell. She seemed to be laying eggs, piling up a clump of little whitish cylinders.


The video function of my camera was running at this point, so I had a good close-up view on the screen. To my surprise, the cylinders moved and crawled deeper into the center of the flower. Not eggs. The fly was giving birth to live maggots. (Now I've learned that all members of the family Sarcophagidae are larviparous or ovoviviparous). Under normal circumstances, this would give the maggots a head-start over other consumers of the limited resource that they depend on. Little Burrowing Beetles for example have a slower start, being deposited in egg-form, but then they can rely on the tender loving care of both their parents, a luxury the flies have to do without.
But under normal circumstances, I never would have had my camera positioned so close to an egg-laying flesh fly. Recording it it on a flower instead of on rotting flesh made all the difference. 
These larvae, though, are condemned to starve to death in the heart of the flower because their mother fell fore the deception of a devious plant. With them, the offspring of the parasitic wasp (a Sarcophgid specialist) is also bound to die.

A Green Bottle Fly has also arrived (left)
 We often think of pollination as this beautiful system of symbiosis between plants and insects, with dutiful bees doing their part, being then so richly rewarded that they don't mind sharing with yet another symbiont, the bee keeper (or should we call him a parasite of the system?)
In reality, plants have evolved to propagate their genes. That's it. They may pay for pollination services with nectar, drugs (Datura and Manduca) sex (Bumblee Ophris and hymenoptera) or let little fly-babies starve to death. The plant does not care!

I thought I'd also add a photo of the 'normal' situation. Here a  carrion beetle, Thanatophilus truncatus, a blow fly,  Calliphoridae and again a parasitic wasp, Braconidae have found a dead deer calf. They were the first to arrive in the morning after the deer had been run over by a car at night. Their larvae will act as macro-decomposer, opening the way for bacteria and fungi. This is a very important role for insects in the ecological system.

Sunday, October 5, 2014

Hot Peppers

At the beginning of summer one of our big box stores was offering all kinds of little pepper plants for next to nothing. So we probably took home more than we will ever want to eat.
The plants grew very well in pots on the patio where they used to get morning sun and then shade from the roof as the sun rose to the zenith. Now that autumn is upon us Arizona still gets hot, but the sun rays come in at an angle that exposes the peppers to so many more hours of light and heat that actually have to water them twice a day.

With the help of our nitrogen rich compost and some doses of Epson Salt to replenish the soil's magnesium the plants are growing beautifully. While the Jalopenos are towering over my head by now, Tabasco and Cayenne have turned into more delicate and very ornamental plants, studded with colorful small fruits. My old volunteer bell pepper plants are also constantly producing small but tasty pods. We are very much enjoying a wall of healthy green leaves that we already shared with two generations of leaf-cutter bees.

No one else has attacked our pepper plants yet. That somewhat surprises me because they have close relatives in our ecosystem, the red, spicy, pee-sized chiltepins, so they should have natural consumers.  'Of course', the Tucson Backyard Gardeners say 'Their spiciness protects them'. With this in mind, the gardeners produce concoctions of hot pepper that they then spray on all kinds of plants to prevent all kinds of  'pests'.
It sometimes works, probably because they usually add more than one ingredient to their 'organic pesticide' so it's never clear which component is actually effective. Or the pest was the household dog, and dogs do not like pepper spray  in their sensitive noses. But......

The ingredient that makes peppers hot and spicy and in high concentrations irritating to mucous membranes is called Capsaicin. It is present throughout the fruit and most concentrated in the placental membranes where the seeds are attached.
Capsaicin is known to stimulate temperature and pain receptors in mammals (like rodents, dogs, humans and bears). 
When I was working at my Ph. D. at the Max Planck Institute in Bad Nauheim, Germany, a friend of mine, Herbert Schmidt, tested the effect of capsaicin on  birds (he is an electro-physiologist and worked on tissue samples). He could show that while mammalian thermo and pain receptors both responded to capsaicin applications  (some of its therapeutic value is based on that effect), a similar response to capsaicin was not found in bird tissue.

When I came to Arizona, the folks at Native seed Search offered a plausible explanation: The red, attractive fruit of chiltepins, tabasco, jalopeno et all are probably exposed to several kinds of 'harvesters': Small mammals like packrats and mice, big mammals like javelinas, bears and humans, and birds.
Plants produce fruit to disperse their seeds. Many are juicy and inviting to attract animals to do the job, carry the fruit away, eat the juicy flesh but hopefully leave the seeds unharmed.  But if  rodents would feast on peppers, they would probably eat the juicy flesh and also chew up the seeds. This would destroy them and make them useless for plant propagation. So pepper plants evolved to load the fruit with capsaicin to make them rather impalatable to rats, squirrels et al.

But that's not good enough. The seeds are not supposed to just drop down under the mother plant to germinate in its shade and let the seedlings compete with each other. To thrive, they need to be dispersed.  So the inviting fleshy fruit is not a forbidden one to every harvester:  Birds suffer no ill effects at all because their receptors do not react to capsaicin. So they are free to eat the peppers. Not having teeth, they swallow the seeds whole and pass them through their digestive system, planting new pepper plants in their wake.
Perhaps even big mammals who don't bother to crack open every small seed would eventually excrete them in a viable state. The capsaicin response is dose related, meaning that a big bear or human may enjoy a delicate tickle where a small rat would suffer very serious heartburn. So maybe?

Anyway, the bright red, inviting, spicy peppers that signals 'stop' to rodents and other small mammals, can be an invitation to others.
(Sweet bell peppers are the result of selective breeding and do not occur in the wild)

I knew those research results and theories, but until today, the practical experience was missing. Sure, our packrats are leaving the peppers alone, so are our dogs, and we humans love them in small amounts. But the birds???

By the beginning of October, the candle-like upright Tabasco Peppers finally ripen, softening and turning from pale white to orange. (Wind and dogs have been playing with the labels that I was keeping with the pots, so there may have been mix-ups, but it's either serrano, tabasco or cayenne.) Yesterday I noticed that several fruits were shredded open on one side.  

Today during breakfast we finally cought the 'culprit'in the act.  Chattering happily a Verdin was intensely at work in in the Tabasco plant. Catching insects? Snacking on nectar from the few remaining flowers? No. He was going for the fruit. He devoured the fruit flesh and happily pecked at the seeds. Half a day later, most of the orange fruit were more or less gone, seeds and all.

 I am happy to have finally witnessed the story in real life and I am also glad that just a day earlier I had the bright idea to finally pick a bunch of peppers and pickle them in sweet vinegar.  

Friday, October 3, 2014

Toxic Shocker?

The BBC  recently acquired one of my spider photos for the October issue of their Wildlife magazine. The blurb with it was 'shockingly' racy and hyped up in true mass media fashion.

But the source link under the article lead to a publication of solid electrophysiology in Nature Communications:

Niraj S. Bende, Sławomir Dziemborowicz, Mehdi Mobli, Volker Herzig, John Gilchrist, Jordan Wagner, Graham M. Nicholson, Glenn F. King, Frank Bosmans
Nature Communications 5, Article number:4350
Abstract: β-Diguetoxin-Dc1a (​Dc1a) is a toxin from the desert bush spider Diguetia canities that incapacitates insects at concentrations that are non-toxic to mammals. ​Dc1a promotes opening of German cockroach voltage-gated sodium (Nav) channels (​BgNav1), whereas human Nav channels are insensitive. Here, by transplanting commonly targeted S3b–S4 paddle motifs within ​BgNav1 voltage sensors into ​Kv2.1, we find that ​Dc1a interacts with the domain II voltage sensor. In contrast, ​Dc1a has little effect on sodium currents mediated by ​PaNav1 channels from the American cockroach even though their domain II paddle motifs are identical. When exploring regions responsible for ​PaNav1 resistance to ​Dc1a, we identified two residues within the ​BgNav1 domain II S1–S2 loop that when mutated to their ​PaNav1 counterparts drastically reduce toxin susceptibility. Overall, our results reveal a distinct region within insect Nav channels that helps determine ​Dc1a sensitivity, a concept that will be valuable for the design of insect-selective insecticides.

I am of course glad to have my image associated with this research, even through a magazine that tries to make science palatable by using racy come-ons. Though how many readers will make it at least as far as the abstract?