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| Antennae divide the eye in two! |
Patrolling our backyard milkweed I came across this beetle. It was colorful, red with sharp black spots and had black antennae almost as long as its body, identifying it as a member of the Cerambycidae family of Long Horn Beetles. Back to INaturalist and out jumped the Red Milkweed Beetle. Its scientific name is Tetraopes tetrophthalmus meaning “four-eyed” twice! Each eye is divided by an antenna base, making each eye look like two.
The
adults feed on sap from the leaf veins where the toxic latex is more
dilute. Both they and the larvae feeding on the roots acquire some of
the toxin which they advertise with their red aposematic colors. When
startled they make a shrill noise and when interacting with another
beetle, they make a 'purring' noise. I lost that hearing range decades
ago and will have to take the word of the entomologist audiologists.
On the next milkweed there was similar looking colorful beetle. At first glance it looked the same but on photographs later I could see it had short antennae and the long snout of a weevil. There were distinctive markings including a black diamond on the pronotum, easily identifying it on INaturalist as a Cocklebur Weevil, Rhodobaenus quinquepunctatus. It likely won't harm the milkweed as its larvae feed on cocklebur stems only.
The trademark 'snout' or 'nose' on the face identifies it as a weevil. This type of beetle uses that long rostrum to chew into plants. Without the long nose you can be sure that you "see no weevil." Their larvae normally feed on plants like sunflowers, cocklebur, and ragweed and it may have been just passing through and stopped for a rest.
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| Melanic form - Bugguide |
This Cocklebur Weevil has another cool trait. A few have a melanic phase where the elytra are dark or even black. This is the only Rhodobaenus species in North America that has this trait.
Some other milkweed longhorns are discussed on this MDC site.
