Here are photos of a gorgeous Iron Cross Blister Beetle (Tegrodera aloga) that I saw one afternoon in Tucson. This was in early May of 2005, on the Cactus Forest Loop of Saguaro National Park East, at perhaps 3000′ elevation. The vegetation was starting to dry out, and the beetle was stopping to eat at the remains of flowers that I think were Woollystar (Eriastrum) flowers.
It would eat at one of the remains of the flower heads for a few minutes, then climb down and walk to the next one. There wasn’t a lot of vegetation left for it to eat – just a few bits of green and lots of the ‘wool’ from the flowers.
You can see a fragment of green vegetation just above the beetle’s head in the photo below.
The beetle was about an inch long, and it was brilliantly colored. It seemed to almost pop from the desert floor, it was so bright and shiny.
I was reminded of these beetles while I was writing a recent post on an Oil Beetle from the mountains of Colorado. Both of these beetles are Blister Beetles – members of the family Meloidae. Both of them produce and sequester the toxic chemical cantharadin.
But their appearances and behavior are so vastly different – the Oil Beetle is shiny black, kind of corpulent-looking and slow, while the Iron Cross Beetle is svelte, and quite active.
From what I’ve read, the Iron Cross beetles tend to be patchily distributed in time and space. Some years you’ll see a lot of them in a particular area, then maybe you won’t see them there again for a number more years.
Iron Cross Blister Beetles are thought to be parasites of Solitary Bees. The beetle’s strange (and kind of creepy) triungulin larva hitch rides on female Bees back to the bee’s nest. There, the triungulins eat the bee’s larva, and the nectar and pollen that the bee had stored for the bee larva.
As far as I can tell, though, that part of the Iron Cross Blister Beetle’s life cycle is mostly extrapolated from the beetle’s taxonomic relatives. I haven’t been able to find information where that has actually been observed.
I was quite surprised at how much is not known about these beetles. A beetle as flashy-looking as this, I would have thought there would have been a ton of research on its ecology. I would imagine that its patchy distribution in time and space would make them difficult to study.
It’s astonishing how much there is still to find out about the world. And kind of cool, too.
Sources:
Evans, Arthur V. 2021. Beetles of Western North America. Princeton University Press (September 28, 2021). ISBN 0691164282.
Marshall, Stephen A. 2018. Beetles: The Natural History and Diversity of Coleoptera. Firefly Books; Illustrated Edition (September 1, 2018). ISBN 0228100690.
Werner, Floyd G. and Carl Olson. 1994. Learning About and Living with Insects of the Southwest: How to Identify Helpful, Harmful and Venomous Insects. Fisher Books, First Edition. ISBN 1555610609.
Bugguide.net’s page on the Genus Tegroda.
