Fire-colored beetle (pictured is Genus Pedilus)
Strap yourselves in because this week’s crawly takes wickedly weird up a notch! Meet the fire-colored beetle (pictured is Genus Pedilus).
There are 50 species of fire-colored beetles (Family Pyrochroidae) in North America. Pyrochroidae is from the Greek pyros which means fire and chroma meaning color. Interestingly, few of the 50 species are truly “fire” colored. Most are black with a red head or a red neck. The few fiery ones are bright red.
Our pictured fire-colored also fits the name nicely with their marbled elytra glowing like tiger’s eye stones.
Overall, fire-colored beetles are small (just over one-eighth of an inch) unassuming critters easily overlooked, but worth looking at.
When it comes to arthropods, black and red coloring sends the message “Do not eat me, or you will be sorry!” This is known as aposematic (warning) coloring. Many arthropods who sport these warning colors are faking it. They aren’t truly poisonous but want predators to think they are.
Fire-colored beetles aren’t naturally poisonous, but they’ve found a heck of a workaround to that problem – they are cantharidiphiles.
A cantharidiphile seeks out blister beetles (Meloidae), who naturally produce cantharidin.
Cantharidin is a highly toxic compound. It is odorless (to humans) and can be colorless, though some blister beetles add color to it. Topically it can cause severe blisters to skin which can take over 10 days to heal. Ingested, it’s deadly. It is classified as an “extremely hazardous substance” in the United States.
If ingested, just 10 milligrams of cantharidin can be fatal. Naturally, the bygone aphrodisiac “Spanish Fly” was made from ground up blister beetles – cantharidin and all – because humans make questionable decisions sometimes.
That said, fire-colored beetles make clever decisions. They have an immunity to cantharidin and use that to their procreative advantage.
Male fire-coloreds will seek out blister beetles and mildly pester them by either chewing on the blister beetles’ elytra or nipping at their legs. Blister beetles are six times larger than fire-colored beetles, so they aren’t harmed, but are annoyed enough to emit a dose of cantharidin.
Fire-colored males then take the cantharidin and store it in tiny grooves near their antennae. Female fire-coloreds will sniff various males, and if a male doesn’t have that cantharidin dose, it’s “See ya!” and the female will search until she finds a male with the toxin in store.
The males transfer the toxin to the females who are then able to lay cantharidin-coated eggs. Females lay those eggs under the bark of dead trees and other carnivorous beetle larvae also living there take a hard pass on the “coated eggs of death.”
It isn’t known whether the cantharidin is also present in the fire-beetles’ larvae. Little is known about the larvae, except they live under dead tree bark until they are ready to morph into adult form. The larvae may be carnivores, or they may go in for fungus as a main dish.
Adult fire-coloreds most likely feed on pollen and nectar as they are generally found on flowers. Because any given adult may have a dose of cantharidin on or in them, those warning colors may be a true warning.
So, enjoy looking at any fire-colored beetles you see this summer, but don’t eat any.