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Beetles are the largest order of insects. The 400,000 types of beetles on Earth make up about 25 percent of all animal species! You probably see them all the time – from ladybugs to fireflies to carpet beetles. Many are helpful, eating aphids or other pests. Others, like the emerald ash borer, can cause significant damage.
The tumbling flower beetle (family Mordellidae) is helpful. Also called the pintail beetle, it is renowned for its tumbling, flipping, turning and jumping motions when it is disturbed or captured. It has large hind legs, which it uses to kick when it is on a hard surface. This kicking causes it to bounce around erratically when agitated. When threatened, it kicks off from a plant, tumbling to the ground. Then it flies away to a safer spot. The disadvantage of this method of protection is that the beetle abandons its feeding site when disturbed.
The tumbling motion of these beetles is actually a series of very rapid hops. The beetle changes directions (tumbles) because it alternates which leg it uses to initiate each hop. It tumbles one direction when kicking off with the right leg and the other direction when kicking off with the left leg. (Each hop lasts 80 milliseconds.)
This beetle has another common name. It is sometimes called a pintail beetle because it has a pointy pin-shaped protrusion on the end of its abdomen. There are about 1,500 species in this family of beetles. These guys are small (about one-quarter of an inch in length), wedge shaped and covered (usually) with silky hairs that can form lines, bands or spots.
The word beetle comes from the Old English word bitela, which means “little biter.” These beetles, especially their larvae, are plant chewers. The offspring (larvae) of tumbling flower beetles live in and feed on the pith of plant stems or rotten wood. The adults feed mostly on nectar and pollen, but they also chew and feed on flowers; however, the damage they cause to flowers is minor and more than offset by their prodigious pollination of the blooms they visit.
Tumbling flower beetles, like all beetles, undergo complete metamorphosis. Like butterflies they have four life stages: egg, larva, pupa and adult. You will see the adults mostly in June and July. You might see the larvae from later summer onward. The larvae go through several molts, overwinter and reemerge in the spring, when each forms a pupa. When the adult beetles emerge in June, they mate. The females then bore into the skin of plant stems where they lay as many as 40 eggs, beginning the process over again.
Tumbling flower beetles play another important role in the ecological cycle. The larvae they produce become food for birds, just at a time birds need to feed their young. The downy woodpecker (and other birds) eat tumbling flower beetle larvae.
Tumbling flower beetles were first identified way back in 1775 by Johann Christian Fabricius (1745–1808), a Danish zoologist and one of the most important entomologists of the 1700s. He believed, among other things, that humans originated from great apes and that two species can hybridize with each other to produce a new species. He also believed that animals can pass on physical characteristics that the parent acquires through use, such as strong muscles. Needless to say, some of his ideas seem dated today, but his work was important.
Fabricius named almost 10,000 insect species and established the basis for modern insect classification. He classified insects using the form of their mouthparts to distinguish between orders. He reasoned that the mouth characteristics developed from each insect’s diet, and that their biology depends on their diet. (Linnaeus, the developer of our modern system for classifying and naming living things, on the other hand, used the number of wings to classify insects.) Fabricius’s system of insect classification laid the foundation for modern entomology.
The ancestors of the tumbling flower beetle were some of the earliest insects that used flowers for food. Thus began the partnership between flowers and beetles: Beetles feed on the pollen of flowering plants, collecting pollen grains on their body as they do so. They pollinate flowers during this process by transporting the pollen grains to other flowers. About 50 native plants in the United States depend solely upon beetle pollination. Some plants that beetles pollinate include magnolias, tulip trees and water lilies. In addition, beetles help to pollinate goldenrod, meadowsweet, spicebush, yarrow and sunflowers.
All insects are poikilothermic, which means their internal temperature varies a great deal. They can withstand our cold winters and hot summers. For this reason and because they are so numerous, beetles are indicators of habitat quality. If their numbers decrease, this can be an indication that something is amiss.
So in your travels, keep your eyes peeled for beetles. If you spot a tiny quarter-inch beetle with a spike on its abdomen, you have likely discovered a pintail beetle. If you watch it closely, you may be rewarded by its acrobatic tumbling movements.
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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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