Urban Society (of Insects)

Last Friday my colleague Gene Hall showed me some Monarch caterpillars that are growing up on Desert Milkweed plants on campus.

The plants are snug against the south-exposed brick wall of the Chemistry Building, so if the caterpillars survive the periodic drastic clipping by U of A gardeners, they have found a microhabitat that will sustain them even during the colder weeks of winter.
We found very small caterpillars around a centimeter in length, probably second instar, and a few that were more than an inch long, indicating that at least two females were ovipositing here lately. I did actually see two adult Monarchs in Marana last week. All these observations are data points off the main eastern or western migration route of the majority of Monarchs, but storms displace a number of them each year and we also seem to have some small, but constant populations around Tucson.

 I took the opportunity  to photograph groups of bright yellow Oleander Aphids (Aphis nerii) that commonly feed on milkweeds. Besides hundreds of wingless individuals one group also included a few winged females. One of them was very freshly molted and teneral, with still soft wings and without mature pigmentation. (I will try to describe the complexities of Aphid reproduction and generation sequence in another chapter).

On the enlarged images I later discovered a syrphid larva that was feeding on the aphids (bottom left). It was nearly transparent and moved inconspicuously among its victims.

The syrphid larva could be the offspring of the male  Bird Hoverfly that I had photographed a couple of days before in the same area.

An only  2 mm long Dusky-colored Ladybug, a species in the genus Scymnus, was also preying on the smaller aphids.

During the photo session, an Ichneumon Wasp appeared. It flew around the milkweed stalks as if searching for something, and I assumed that the parasitic wasp was planning to lay its eggs one of the Monarch caterpillars. When it landed very shortly, I managed only one unfocused shot, just for documentation. But it was enough: from the blurry image plus the description of the situation Bob Carlson on Bugguide was able to narrow down the identification to the subfamily Diplazontinae. All species of this group are believed to be parasitoids of syrphid larvae.

So with our short lunch hour excursion and some follow-up research we had discovered a whole complex ecosystem of herbivores, predators, and a parasite of the predator. All that right next to the wall of the Chemistry building, in an unpaved area that is only a few inches wide.

In the interest of full disclosure, there were also two ornate Tree Lizards, several Small Milkweed Bug nymphs, a Gray Bird Grasshopper and a  Smoke Tree Sharpshooter hanging out among the milkweeds.  Some, like the bug nymph, were there to sip the chemical cocktail provided by the milkweeds, others probably mostly to get warm on the sun-exposed bricks. Either way, it takes care of the energy budget.

Cedar Waxwings at Agua Caliente in Tucson

Super Bowl Sunday at Aqua Caliente in Tucson: The Plague Birds (Pestvogel) are here. That's what the beautiful waxwings were called in Holland where I first saw them, the Bohemian Waxwing in that case. Medieval Europeans were pessimists by default. Wars, starvation, and worst of all, the plague were recurring catastrophes that nearly every generation could expect to experience. Every sudden change from the usual was seen as a harbinger of disaster. Waxwings are birds of the northern forests where they breed in large groups without individual territories. During non-breeding times they do not really migrate, but given the right conditions, they may form large swarms  that stray opportunistically into orchards or into southern areas with good berry crops. So when, every decade or so, they suddenly appeared in such masses that they were hard to miss, the Dutch took their sudden arrival as a sign of the plague.

Bohemian Waxwings in Germany

 The name Seidenschwanz (Silk Tail) in German refers to their silky plumage. This was translated into the Latin Bombicylla as the scientific name of the genus. On the wings of both the Bohemian and Cedar Waxwing  the red shaft-ends of some feathers extend beyond the barbs and look like sealing wax,  hence the English name Waxwing.

Cedar Waxwings in Gainesville, Florida, Watercolor 1991

 Like their European cousins, the American Cedar Waxwings are no true long distance migrants, but the flocks  rather opportunistically  appear at places with a rich supply of fruit. In Florida I have seen them show up to feast on ripe palmetto berries, last autumn  the mulberry trees between Green Valley and Madera Canyon were full of the birds, and now they are all over the Washingtonia Palms at Agua Caliente on Tucson's Northeast side to pick the abundance of little black miniature dates. Both mulberries and Washingtonia Palms are introduced to the desert. I am wondering how the birds originally found them, and whether there is some kind of shared flock memory that helps them find the food sources again in years of need. Perhaps the flocks originally came to feed on something more native like the berries of the Madrone Trees in the Santa Rita Mountains.

Anyway, last Sunday there was a lot of action in drooping bundles of tiny black dates that provided a nice background for the subtlety colorful birds.

About 200 birds were taking turns between feeding bouts and breaks in the nearby Salt Cedars.

They started feeding in shady spots under overhanging palm fronds when I still felt rather chilly, so if you want good sun exposure for photos, you have to get there early. Sometimes, though,  colors are truer in the shade than in the harsh sunlight.

Some very feisty Robins were also gorging themselves - hanging in the palms as well as collecting the berries from the ground.

A Common Yellow-rumped Warbler posed nicely - I have a foggy memory of a Robert Bateman painting just like this.
A Sora visited shortly and on the back path I saw and heard a Beardless Tyrannulet but another birder was pursuing it with a better camera, so I didn't want to push too close with my short lens.

Thanks to Lois Manowitz  whose flickr photos alerted me to the Waxwing invasion!

Sure Signs of Spring

An old pecan grove at the Pinal Airfield used to be a great attraction to migrating birds, a so called migrant trap. But the irrigation of that grove has been so reduced over the last years that most of the trees died. So there were not many birds, but lots of fallen branches on the ground to give insects shelter. Tellingly, several woodpeckers and a Say's Phoebe were searching for prey.

I turned some wood and found a tenebrionid beetle Triorophus sp., and a juvenile Labidura riparia (Shore Earwig) that was hiding in something reminding of the pupal chamber of a beetle. Next, I discovered several Pillbugs and a very shrunken, discolored lizard. 

Then something moved and climbed onto my hand. A moth with only stubs for wings. It's color identified it as a newly eclosed Salt Marsh Moth whose wings were still very undeveloped.

Shed skin of a caterpillar (exuvia) and pupal cocoon shown next to an adult moth 

Earlier I had found many hairy, dried caterpillar exuviae that were left from the molt that initiated pupation last fall.  The moths then hibernated in the pupa stage (Moths are, like Butterflies, holometabolic, meaning their developmental stages start with the egg, proceed through several stages as a ever growing caterpillar, to the pupa from which emerges eventually the fully formed, but not yet fully 'inflated' adult moth).

The young Salt Marsh Moth inflated its wings in a little more than 1/2 hour

The young moth squirted a stream of brown liquid on my hand, the meconium. The meconium is usually expelled when the wings are fully inflated, so I was worried that I had disturbed the moth at a critical time and caused it to lose too much fluid too early, but as I watched, the wings stretched and grew and started to resemble their final shape. To aid the process, the moth moved into a position which allowed gravity to help inflating the wings and folded them like a butterfly would - a position that is rarely seen in this moth after the wings are hardened. 

Estigmene acrea (Salt Marsh Moth - Hodges#8131) The color of the caterpillars is variable

 I have raised other moths from caterpillars before, and although I find the process magical and very worth watching, I usually miss the last stages of wing stretching because it just takes too long. This active little guy went from 'wingless worm' to flight-ready moth in little more than half an hour. 

By then the young earwig had withdrawn into a crevice, the darkling beetle was still looking for a shady place, and the lizard had recovered in the warm sunshine, filled out his wrinkly skin and regained the color pattern of his species,  the Ornate Tree Lizard.

Packrats in our Compost Bin and in Science

 In all biological questions, my husband usually refers to me. The latest was: "what do you want to do about the rat in the compost bin?"

In kitchen and yard, we religiously save all scraps of organic material to let them decompose into fertile soil in two upside down garbage bins that sit with their openings on the ground.

It works - industrious Turkestan Roaches seem to be doing a lot of the early break down, and that's no problem because the bins are far from the house in an old 4H-goat pen. The fence keeps out our Husky, Javelinas, Coyotes and Foxes, and rows of bricks around the bottom of both bins prevent most rodent intrusions. Somebody once chewed right through the plastic wall - so now there is a hardware cloth patch.

But for a couple of days there had been a packrat sitting in the cockaigne of lettuce leaves, cucumber seeds, carrot pieces, and onion peels. Gray and big eared, she wasn't shy at all - just glared at me from under the lid of the bin. I knew that my friend Ned Harris was looking for a packrat photo opportunity,  but I could tell that this background wasn't quite it.  So, a photo for myself (I'm much less critical than he) and then the release of the rat. First I tried to lift her by the tail like a white lab rat, but she desperately clung to the substrate and I could feel that the tail's loose sheet of skin would be sacrificed before I could dislodge the animal. So I just coaxed her onto a trowel, lifted her up to the rim of the bin and let her hop off . I wouldn't  try that with a wild Brown Rat (Rattus norvegicus). But this was a White-throated Packrat (Neotoma albigula), and I had noticed before that our resident females are rather calm-natured.  So now she can get back to her business of collecting Randy's cactus clippings to decorate her home. Notice those fences around single pots in the photo above? That's how we try to protect our favorites.

Photo by Doris Evans

All over the Americas, there are many species of packrats. Our backyard with its scattering of Creosote bushes and cacti is the ideal habitat for the local species Neotoma albigula, the White-throated Packrat, and not even our five dogs and two mostly indoor cats seem to be much of a deterrent.

We live in an uneasy truce with the rodents. As the name says: they collect stuff to pile on top of their nests. But the nest can be in the down-spouts of our rain gutter with lots of collectibles left on the living room window sill that happens to be part of the way to the roof. That rat had to be evicted twice.

Another one added parts of the start-plug cables of my car to its midden. I used to park in the shade of a large Ironwood Tree. As the rats prefer working in the dark of the night, I now park over special, photocell-activated lights that Randy has sunk into the driveway. So far no further electrical disasters to report.

Pack rats are also carriers of several transmittable diseases. Hanta Virus has been found in Pima County Neotoma populations, but since we are (hopefully) never exposed to a room full of dried, pulverized, airborne rat droppings that are the most likely source of infection, there seems to be no problem.

Kissing Bug, Triatoma rubida, adult and nymph

Pack rats middens are also the favorite breeding ground of Kissing Bugs. Every summer night we can find several of those, usually engorged with blood from our dogs,  around patio lights or my black light. Kissing Bugs are part of the Assassin Bug family Reduviidae. Adults usually appear from May to early July and disappear during the monsoon season. Immatures have been found crawling around even in winter. These bugs bite rats, dogs and people alike to drink their blood. They attack at night and use an anesthetic, so their bite goes unnoticed. If you don't get allergic (which can happen after repeated exposure) there seems to be no reaction to the bite itself, no itching or swelling. But Kissing Bugs can transfer the tropical flagellate protozoan Trypanosoma cruzi that causes Chagas disease. This parasite has been found in Arizona packrats. Luckily our local Kissing Bug species Triatoma rubida seem to abstain from behaviors that would transmit the parasite. (I will get back to Kissing Bugs in later blog).

Packrat populations may also attract rattlesnakes. Indeed, we had a big old Diamondback living in the entrance of a midden. I couldn't tell whether he shared it with the rats or whether he had already devoured his hosts. We were acquainted with him for years until he scared me several times too badly - by being nice, really: he just didn't rattle anymore when I was out there single-mindedly concentrating on my photography, and several times I found his big head less than a foot from my ankle or my dogs' paws. The midden in question was under a big old opuntia. I finally lost my nerve and we relocated the snake to the state land. It took less than one summer for the rats to destroy the cactus.

So there are plenty of reasons to dislike packrats. But I can't help finding them also entertaining and fascinating.

Pear Pads with Rodent damage                                                Javelina bites leave torn fibers behind

Low desert packrat species share their extremely arid and hot habitat, without access to fresh water, with a masters of desert survival, the Kangaroo Rat. But while K-rats can live on dry seeds thanks to the enormous concentration capacity of their kidneys,  packrats void copious urine.  Thus they are only able to maintain their water balance as long as they have access to their favorite high-water-content food, succulent plants like cacti and agave (Schmidt-Nielson and Schmidt-Nielson, 1952).

Middens are usually shaded by vegetation, but sometimes the rats bite of the cactus under which the nest

Their most special adaptation, which gives packrats their name and makes it possible for them to live in very hostile environments, is their ability to construct huge, insulating middens. Packrats seek rock crevices, caves or dense patches of vegetation as shelters, but they improve these by piling on sticks, pieces of cacti, bones, spent shells from guns, toys - just about anything portable that catches their eye. These piles can be conspicuous and over 2 m high in some species. Underneath this fortified den that protects from predators and buffers against temperature extremes is a burrow system with chambers serving to cache food (Packrats do not hibernate) and the small nest made from soft, shredded material.

 When we evicted the 'down-spout-rat' by turning on the water-hose I was surprised that it showed neither fear nor aggression even when cornered. Now I observed the same 'tame' behavior in our compost-bin guest. This character has probably evolved in packrats because the fortified den is a save haven for this animal that has no energy to spare for fight or flight. Packrats live under chronic energy stress due to their diet of low energy plant material (Cactus, Creosote, Juniper) much of which is also rather indigestible because it is loaded with defensive chemicals like terpenoids.  (McClure and Randolph, 1980).

Amberat, a treasure to science
So Packrats are extremely faithful to these middens that their survival depends on. Good den-sites are in short supply and the accumulation of material is costly, so generation after generation of the female line uses the same den, adding material and caching food. Over years, decades, centuries, even millennia, urine accumulated and dried in amber-like clumps under the nest - this substance is called amberat (Some starving miners around 1849 actually tried to eat the 'candy-like food'). 
Today, paleontologists and archaeologists are finding the Southwestern packrat middens a plethora of valuable information. Fossil plant pollen are imbedded in amber-like urine deposits and the whole den  is a collection of animal and plant records that reach far back into the Pleistocene.
As there are no pollen-preserving peat bogs in the Southwestern deserts, and pollen studies were limited to lake sediments in only a few locations, the study of packrat middens became one of the most important resources for the understanding of the changing biogeography of the Southwest from the Pleistocene to the present.

Literature: 
JL Betancourt, TR Van Devender, PS Martin (1990) Packrat Middens, the Last 40,000 Years of Biotic Change.  University of Arizona Press, Tucson
K Schmidt-Nielson,  B Schmidt-Nielson (1952) Water metabolism of desert animals , Physiological Review 32, 135-166
P A McClure, J C Randolph (1980) Relative allocation of energy to growth and development of homeothermy in Neotoma floridana and Sigmodon hispidus. Ecological Monographs 50, 199-219 

Wintering Birds in Avra Valley and Santa Cruz Flats

 Pima Cotton, Sorghum and Alfalfa: the Avra Valley north of Marana is flat, fertile, irrigated and heavily used for agriculture.

Dust, pesticide and herbicide bombardment and unrelenting sunshine without shade can be a real turn-off at times, so I hardly ever go there.

Migratory birds have different preferences. Thousands of Blackbirds, mostly Yellow-headed, and Lark Buntings land in freshly harvested sorghum fields.

Yellow-headed Blackbirds

Lark Buntings

Lark Sparrows

Horned Lark

Northern Harrier

Common Ground Doves

 Scores of other sparrows and Meadow Larks, too shy for good photos. But Lark Sparrows sit nicely in great light. On the side of the irrigation ditch a single Horned Lark, but I have to shoot through the windshield. Same for the Northern Harrier. Other raptors show up and disappear before I get a good look. Lots of Ravens. Little Ground Doves are courting. Spring is coming.