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What Time is it in Nature: Red Milkweed Beetle

June 20, 2014

There are massive numbers of insects out and about at Prairie Ridge currently!  The Common Milkweed is an especially good place to look for insects as you can find many species using each plant including aphids, Milkweed Bugs, predatory maggots, lacewing larvae, and several beetles.  One of the most easily recognizable beetles is the Red Milkweed Beetle, Tetraopes tetrophthalmus.

Red milkweed beetle on milkweed

Red Milkweed Beetles, often called RMBs for short, are members of the longhorn beetle family Cerambycidae and are common prairie and grassland beetles in the eastern US.  Like their longhorn beetle relative, RMBs have antennae about as long as the length of their bodies which, not including the antennae, is generally 12-15mm long (a little over a half-inch).  RMBs have black antennae and legs, but the rest of their body is a brilliant orange-red with distinct black markings on the thorax and elytra, the hardened upper pair of wings that covers the abdomen.  You will often find these on and around Common Milkweed, though occasionally you may spot them on other milkweed varieties as well.

RMBs spend nearly their whole lives around Common Milkweed.  Males and females find one another wandering among the Milkweed leaves in early summer and will mate.  The female will then lay her eggs at the base of a Milkweed stem, sometimes inserting her eggs into the stem itself, or on a piece of grass close by.  Once the larvae hatch, they will move down to the roots of the Milkweed, either tunneling just underneath the surface of the stem or through the soil.  The larvae feed on the roots as they grow though the early fall.  They will stop feeding in the winter, but may briefly resume feeding in the spring before building a small chamber in the soil near the Milkweed and pupating.  They will then emerge a month later as adults.

Like the larvae, the adult RMBs also feed on Common Milkweed, though they focus on the parts of the plant above ground such as the leaves, flowers, and buds.  Like many other Milkweed feeders, the RMBs will cut a slit into the leaf vein above the site where they are feeding so that the sticky latex sap (the “milk” of the Milkweed) will drain out.  If enough latex is consumed or is left to dry on the mouthparts, the unlucky RMB may find itself with its mouth glued shut.  Cutting the leaf vein reduces their latex exposure and consumption considerably, though you will sometimes see the beetles rubbing their faces on the leaves in an attempt to scrape the latex off before it dries and hardens.  In addition to latex, Milkweeds also contains powerful toxins that repel most birds and mammals.  Like many other insects that feed on Common Milkweed, other milkweeds, or other toxic plants, the red and black coloration of RMBs is thought to advertise the plant toxins they store inside themselves and their unpalatability to any creature that attempts to eat them.

The scientific name of the Red Milkweed Beetle, Tetraopes tetrophthalmus, refers to a cool characteristic of these charismatic beetles.  Like other longhorn beetles, the antennae are located near the eyes of the beetles.  In many longhorn beetles, they are so close that you will see the eyes wrapped around the base of the antennae.  In the RMBs, the antennae completely bisect the eyes, splitting each eye into two parts.  Both Tetraopes and tetrophthalmus refer to the fact that these beetles have four eyes!

You can find Red Milkweed Beetles all over Prairie Ridge this summer!  Simply look for the Common Milkweed plants scattered across the ground on your next visit (there are two big patches just outside the Nature Neighborhood Garden) and look for red and black.  You might also find some Seven-spotted or Asian Multicolored Ladybugs hiding in the leaves, but you are sure to see many four-eyed RMBs if you look!

What Time is it in Nature is a weekly feature highlighting the current plants, animals, and other wildlife at the Musuem’s public outdoor facility, Prairie Ridge Ecostation. Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive!

Photo by Chris Goforth.

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