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It’s In Your Nature: Many insects use complete metamorphosis

Published September 14. 2024 09:21AM

Insects are invertebrates, referring to their lack of internal skeletons and spinal columns.

Most grow rapidly, but with their “skeletons” on the outside of the body, they can undergo some unusual changes.

Grasshoppers, crickets and cicadas use a three-stage process to mature called incomplete metamorphosis. The young grasshopper looks much like the adult, smaller but with no wings. After molting a few times, it becomes mature and has developed wings.

But many insects use complete metamorphosis. This is a four-stage process: egg, larva, pupa and adult.

Unlike incomplete metamorphosis, where the young somewhat resemble the adult, the larval stage of complete metamorphosis does not. A prime example are maggots. They are the larvae of a house fly or blue bottle fly. These maggots certainly bear no resemblance to the adult.

Another difference between a larva and adult is their diets.

A grasshopper nymph will eat plant material and when it matures, feeds on grasses, weeds or grains. So will the adult.

But not all nymphs feed the same as adults. One extreme example of something different is the periodical cicada (the 17-year “locust”).

After cicadas mate, the female makes a slit in a young twig of a tree and deposits her eggs, which kills the twig. The dead twig drops to the ground, where the eggs hatch, begin feeding on juices in plant roots and emerge in 17 years, shed their exoskeleton one last time and are now adults. The adult cicada doesn’t even feed.

Insect larvae are often voracious feeders. Caterpillars are a good example.

Next to our garden, we plant a number of planters with dill, not for their culinary value but because they are one of the main food sources for the swallowtail butterfly larvae. In a planter with maybe eight or 10 dill plants, four or five caterpillars make short work of the foliage. If they eat all the available dill, we move one or two of the caterpillars to another pot so they have enough to eat.

Caterpillars, as expected of all insect larvae, look nothing like the beautiful adult. Grubs in your lawns may be eating your grass roots and later emerge as either Japanese or Asiatic garden beetles. Those grubs are larvae.

Another non-lookalike is the larva of a mosquito.

If you have a rain barrel or a bucket you forgot in your backyard, look for quarter-inch-long squiggly critters moving around in the stagnant water. These wigglers, mosquito larvae, have a breathing tube at the end of their abdomen, and they swim upward to the water’s surface to snorkel air. They feed on detritus in the water and look nothing like the mosquito that inserts its proboscis deftly in you or your dog’s skin to get a blood meal.

Test Your Outdoor Knowledge: True or False: Only female mosquitoes feed on blood.

Last Week’s Trivia Answer: The familiar nighttime sounds crickets make rubbing their wings together are called stridulations.

Nature Notes: Look for the tupelo (black gum) showing off its scarlet leaves, note the big drop of black walnuts and shagbark hickory nuts, and the big push of tree swallows migrating through this area. And keep those hummingbird feeders up, even though most nesting hummers have moved south. Northern migrants could use that sugar boost.

Email Barry Reed at breed71@gmail.com

I thought this would be an ideal time to remind people that the dense white “nests” in fruit and wild cherry trees in spring are Eastern tent caterpillars, as shown here. The autumn-appearing and less-dense webs are fall webworms. Both larvae will be eating foliage. Less damaging is the fall webworm, since most of a leaf’s production is complete by now.
This is an Eastern tent caterpillar. The larvae will leave the safe confines of the nest, and at about 1½ inches in length will travel to find a spot to make a cocoon and transform to the adult.
You venture out to your garden and discover that one tomato plant has lost half of its leaves. After looking carefully, you find the culprit: one of our largest caterpillars, the tomato hornworm. They can be at least 2½ inches in length.
Some larvae don’t devour your plants. The paper wasp larvae remain safe and snug inside their cells, being fed regularly by the adult wasps. When ready, the larva caps off its cell and pupates there, transforming to an adult wasp.
I found this cecropia moth caterpillar just beginning to form its cocoon last September. It feeds on a variety of vegetation over the summer, and eventually reaches 3½ to 4 inches in size. It will overwinter in the brown cocoon, slowly developing into a moth.
That 4-inch-cecropia caterpillar becomes our largest moth, at about 6 inches in size. BARRY REED/SPECIAL TO THE TIMES NEWS
Popular as a type of fish bait, yellow mealworm larvae will eventually grow into one of many adult darkling beetle species. Normally found eating leaf litter or on your compost, most are raised commercially and sold as bait or food for small animals. But people in some cultures eat them because of their high protein content. BARRY REED/SPECIAL TO THE TIMES NEWS
This larva is probably well known by folks who plant milkweed for monarch butterflies. These pretty monarch butterfly caterpillars don’t try to hide but advertise their noxious taste obtained from eating the milkweed plant’s leaves.
The black swallowtail butterfly caterpillar prefers to feed on plants like Queen Anne’s lace, carrot foliage and especially dill. We have about a dozen caterpillars now in various sizes feeding on the dill we plant almost exclusively to enjoy watching the caterpillars’ rapid growth. When satiated, the larvae leave the planters and find a secure location to make their chrysalis and pupate.
The gypsy moth caterpillars can be devastating to hardwood forests when the population explodes. They are voracious feeders, with many people hearing what sounds like raindrops on the forest floor, which is actually their droppings hitting the dry leaves.
The American dagger moth caterpillar becomes mostly white as autumn approaches. This larva has hairs that can cause skin irritation. They feed on many of our hardwood trees’ leaves, but never enough to cause damage like many other caterpillars. In your outdoor hike in the next week or two, look for these rather “obvious” larvae.