Insect Insights, a Bi-Weekly Buford Blog by Karen Richards

There’s a fairly common beetle you might mistake for two species of beetle. That’s because it’s a dimorphic (= two-formed) beetle, and the male and the female look completely different.

Female Anastrangalia laetifica have rich, deep red elytra with four black spots and males are all black, sometimes with brown tones. 

These are beetles in the Cerambycidae family of longhorn, or long antennae-d, beetles. There are over 36,000 species in the group, worldwide. Some of them have shorter antennae, and many have antennae that emerge right next to or even interfering with the eyes, so that the beetle’s eyes appear to wrap around the antennae. 

Many Cerambycidae also have an unusual mating apparatus. I didn’t know about it until reading up on them one day, then I realized I’d inadvertently taken a photo of it on a pair of dimorphic beetles!

Pair of dimorphic beetles mating, the black male is on top of the red-brown female. They are on top of a flower with a yellow center and white petals.
Photo by Karen Richards

The aedaegus is an internal sac that the male beetle will deploy, by turning it inside out, to deliver sperm to the female. Here, it looks like a nearly clear tube connecting the two beetle abdomens. After mating, the organ will retract into the male and won’t be visible. 

Larvae of longhorn beetles feed on roots, stems or trunks of plants, and they’re called round-headed borers. They have bulging segments, making them look like a short, rounded accordion hose. Because they don’t have legs, those segments help them inch-worm along.

You may see adult dimorphic beetles on flowers this time of year, they’re also pollinators. 

Stay curious!

See more of Karen’s work here.

Sources:

Jim Conrad of Grants Pass wrote a blog post about the aedaegus here: https://www.backyardnature.net/n/a/longhorn.htm. Accessed 7/10/24. 

USDA paper on longhorn beetles: https://www.fs.usda.gov/nrs/pubs/jrnl/2017/nrs_2017_haack_003.pdf. Accessed 7/10/24.