Friday, April 30, 2010

Beetle Paradise at the Santa Cruz River

Over the last sixty years Tucson lost most or all of its riparian habitats due to overuse of the aquifer and droughts. Now there are plans to declare the Santa Cruz River a 'navigable waterway'. ('The federal test of navigability is simply whether the river is usable as a route by the public, even in small craft, and even if it contains obstructions at which boaters get out, walk around, then re-enter the water' Wikipedia). This seems to be the only way to give it at least some protection.Sadly, this pretty picture is misleading. The Santa Cruz River flows year round only because of the effluent from the Water Treatment Facility upstream, and it stinks.

I would not try to navigate this river even in a kayak, and I wouldn't allow my dogs to play in it, but the vegetation on the banks is lush and attractive to insects and therefore to me as an entomologist.

Last week I was on a mission to find little weevils that might live on the Salt Cedars at the Santa Cruz River Bridge at Sanders Road in Marana. Before I reached those trees I spend about 30 minutes on a 30 meter stretch of the river bank.

There, I found a beetle paradise:

Hundreds of Flee Beetles (Altica sp.) had punctured Knotweed Polygonum sp. plants right by the water.

Weevils (Lixus semivittatus) were mating on the stems of very juicy Seep Willow Plants (Baccharis salicifolium)

Little Leaf Beetles of the genus Lexiphanes were hiding between the slightly deformed end leaves of the same plant.

Most impressive, though, was the number of Ladybugs. During my half hour at the river I counted seven species of Coccinellidae:

Most abundant were the Convergent Lady Beetles, Hippodamia convergens.

Adults were mating, and I also found larvae, pupae and freshly emerged adults that were still teneral, meaning their color was still maturing.

Spotted Lady Beetles Coleomegilla maculata seemed to like the umbelliferous plants close to the water. They live on a diet of Aphids and Pollen.

On Willows overhanging the water, Ashy Gray Lady Bugs, Olla-v nigrum, and their larvae feasted on Aphids.

They were joined by the Blood- Red Lady Beetles Cycloneda sanguinea

and their European imigrant cousin, the Seven-spotted Lady Beetle Coccinella septempunctata.

Some scale eating Chilocorus cactus were on the bark of a Mexican Palo Verde Tree.

A tiny Hyperaspis sp. was nearly hidden in the first Mesquite Flowers of the season.

By the way, there were 481 species of Lady Beetles described for North America north of Mexico by 1998.

After being distracted by all these Lady Bugs, I also found the Tamarisk Weevil Coniatus splendidulus that I was looking for, but that will be another blog.


  1. Nice (the beetles, that is -- and the scenery -- I can't smell it from here)! You have a knack for finding the little guys!

  2. I like this blog very much! I would like to do a birdwatching blog and this inspires me keep trying! The information here is interesting, relevant and fun - I look forward to more.

  3. I am glad that someone else thinks the Santa Cruz River in that area is vile! I've done two research projects on aquatic insects that required I actually get IN the river and it was miserable every time. There are hardly any insects in it in the first place, which made it even more lovely. Love the beetle photos though! I'm adding you to my list of links for sure!

  4. Obviously, mine is a hate-love relationship. I've been back several times and found yet another weevil sp. that was new to me