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Red Milkweed Beetle

Caught some Red Milkweed Beetles on a beautiful spring morning in Michigan.

Red Milkweed Beetle archived from: https://uwm.edu/field-station/red-milkweed-beetle/ .....

The RMB’s scientific name,Tetraopes tetrophthalmus, is redundant; both the genus and the species name mean “four eyes” and refer to the way the socket of an antenna divides each compound eye in two, resulting in a lower eye and an upper eye.

Common milkweeds (Asclepias syriaca) are the center of an RMB’s life. In early summer, a female RMB lays her eggs at the base of a milkweed stem, sometimes inserting them into the stem.

Newly-hatched larvae/grubs locate milkweed roots, either by tunneling south beneath the “skin” of the stem or by burrowing through the soil. They dwell in the soil, feeding on milkweed root through early fall (some sources say that they burrow in and feed within the root). They overwinter in the root and may resume feeding briefly in spring before pupating. RMB larvae create earthen chambers to pupate in, from which they emerge a month later as adults.

Adult RMBs eat milkweed leaves, buds, and flowers. Like some other milkweed leaf feeders, they sever leaf veins “upstream” of their feeding site in order to minimize their exposure to the milkweed’s sticky latex; vein severing is shown to decrease latex consumption by up to 92%. When an RMB gets latex on its mouthparts, it cleans them immediately by rubbing its face against the leaf; if it delays, it risks having the latex harden, gluing its mouth shut.

Adult RMBs eat milkweed leaves, buds, and flowers and they can get away with being red and black in a green world because milkweeds are toxic, and so, therefore, are RMBs, and red and black are (chorus of BugFans) aposematic (warning) colors. Apparently, there are some “primitive” species of Tetraopes that are not “locked into” toxic host plants and that have less a conspicuous coloration.

When the milkweeds are thick with females, males (which are smaller than females) become picky, and they favor larger females (plus-sized females have “greater reproductive value”—they pop out more eggs daily and cumulatively). When males outnumber females, males become competitive. Bigger males not only tend to be victorious, they tend to exclude from their smaller brethren all nearby females, not just the maiden in question. Female RMBs don’t send out pheromone signals (perfumes) to attract males, and males don’t use vision to search for females; males simply fly to milkweed plants (the more flowers, the better) and start looking for a little action.

One final endearing trait of RMBs—they vocalize. But, let’s let Richard D. Alexander tell it. In his 1957 paper called “Sound Production and Associated Behavior in Insects,” Alexander wrote that “The red milkweed beetle was first noticed by the writer to make a sound when it was picked up and held. The noise made in this situation is a rather noticeable, shrill squeaking, produced by rubbing together stridulatory [friction-producing] structures on the back of the pronutum and the front of the mesonotum [the upper surfaces of the first and second segments of the thorax]. Several individuals were taken to the laboratory and placed on the leaves and flowers of milkweed (Asclepias sp.) in a quart jar. By listening at the mouth of the jar, one could hear a soft, almost continuous purring noise [oh, Richard—thank you for that image!] … Apparently both sounds are made by both sexes.”

Alexander goes on to say that squeaking is produced when MRBs are held in the fingers, are exploring a cage, are stuck in a milkweed blossom, are placed on or fall on their backs, or are fighting (one beetle is gripping another with its mandibles). RMBs combine squeaking and purring when held in a closed fist, and when two individuals meet and touch antennae or crawl over each other. They will purr when standing motionless; but when they are quietly going about the business of crawling and feeding on milkweeds, they may purr or squeak.

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3 months ago

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bugs · macro · milkweed · plants · michigan

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Camera Information

Aperture f/11
Camera NIKON D800
Focal Length 100 mm
Exposure 1/100 sec

Additional Information

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