Insects and Spiders—Mostly Our Friends

Habitat Enhancing Land Mangement

“Insects are the food that make all the birds and make all the fish. They’re the fabric tethering together every freshwater and terrestrial ecosystem across the planet.”—David Wagner

Christine Middleton

Love them or hate them, insects and spiders are vital to the health of our Texas Hill Country ecosystems. Renowned American biologist E. O. Wilson famously said, “If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.” Insect and spider populations around the world are vanishing. No one disagrees that the populations of many species of insects and spiders are in decline. Just how rapidly is up for debate. A recent study in Germany found significant decreases in the abundance of insects as measured both by their biomass and by the diversity of their species. Another study found that 40% of insect species alive today are vulnerable to extinction.

Why Should We Care?

Humans often characterize these tiny creatures as annoying or destructive. If you watch pest control ads on television, you might think insects and spiders are a huge problem we humans need to do our best to eradicate. Quite the opposite! While some insects are not desirable, especially if you are in the business of growing food crops, most provide ecosystem services we desperately need. And such services are worth a lot. One study estimates their value at US$57 billion per year. Spiders are important too. Globally, spiders kill 400 to 800 million tons of prey a year. Ninety percent of this tonnage is comprised of insects and springtails.

What else do insects do that is so important? Pollination! And not just of agricultural crops. You’ve probably heard that 80-85% of wild flowering plants depend on pollinators for fertilization and that most pollinators are insects. We’re not just talking about butterflies and bees.

A variety of insects, including ants, beetles, moths, flies, and even spiders play a role in the pollination of various plant species. In fact, there are some flowering plants that depend on just a single species for fertilization. Here in Central Texas, a good example is Twisted Leaf Yucca (Yucca rupicola), whose sole pollinator is the aptly named yucca moth.

Insects also play an important part in the decomposition of organic materials to improve soil. They keep our soils healthy by aiding the breakdown and recycling of nutrients from both plants and dead animals. Ants turn and aerate soil, enabling more oxygen to reach plant roots. Ants also carry seeds into their tunnels, and some of those seeds sprout before they can be consumed. Other insects are key to the processing of animal waste—think dung beetles. And you may have noticed the insects that hang around your compost bin. In fact, some cities are experimenting with using insects such as black soldier flies to process food waste.

Predatory insects and spiders play important roles in the natural control of pest populations. Garden stores sell ladybugs to assist gardeners in controlling aphids. Garden spiders also eat aphids as well as gnats, mosquitos and flies. Tarantulas eat lots of crickets, grasshoppers, beetles and caterpillars.

Insects and spiders often become prey themselves. As such they are important elements at the base of many food chains. Some fish, amphibians, reptiles, birds, and mammals are insectivores, meaning they only eat insects. Others also eat spiders. Many animals supplement their diet with insects and spiders, feed them to their young, and/or eat animals who are insectivores.

*The Collapse of Insects* — Julia Janicki, Gloria Dickie, Simon Scarr and Jitesh Chowdhury. Illustrations by Catherine Tai. Published December 6, 2022 by Reuters.com.

The indiscriminate use of pesticides often harms these animals, either killing them directly or through the food they eat. And even if their ingesting harmful chemicals doesn’t kill the animal, it can disrupt their hormones, thus affecting their behavior or their ability to reproduce.

Insect Clues

Identifying insects who share your spaces can be fun and enlightening. Many insects are extremely small, others fly or scurry away quickly, and some only come out at night. If you are lucky enough to be able to photograph them, iNaturalist is a good tool for identifying them. But often you only know insects and spiders are around by the evidence they leave behind. And iNaturalist can help with those clues as well.

So what are some things you might look for? A few species of insects are known for their ability to give live birth to either young or larvae—most notably aphids and blowflies. Some insects carry their eggs with them until they hatch. But most insects lay their eggs on vegetation, in water or on the ground. Some eggs are laid singly, others in rows, and still others in masses of several hundred.

Butterfly eggs are perhaps the easiest to identify because the female butterfly seeks out specific host plants that will support the caterpillars who will hatch. A good reference for associating host plants with the butterflies they support is Native Host Plants for Texas Butterflies by Jim Weber, Lynne Weber, and Roland H. Wauer.

At other times it is the traces left on leaves or other plant parts that indicate insect eggs are or were there. Many insects have a specialized body part called an ovipositor specifically designed for inserting eggs into plant tissue.
Leaf mining insects lay their eggs inside leaves. When their offspring hatch, the larvae live between the two epidermal layers, feeding on the plant tissue in between and leaving a conspicuous trail. That’s usually what has happened when you find a leaf with those conspicuous white squiggly lines.
Insect droppings can resemble coarse black pepper grains. As larvae or adults, insects feeding on plants leave a conspicuous pattern of damage—a hole in a rose bud, bites out of leaves—which, combined with other clues, helps you identify the culprit.

Some plants respond to insect egg laying by forming **galls**. That’s because strange chemicals left behind along with the eggs stimulate highly localized specialized plant growth. It’s somewhat analogous to what happens when a foreign substance is introduced into an oyster and a pearl forms.
Many things cause various types of galls on various parts of plants, including fungi, bacteria, nematodes, or mites. But insects are the main culprits. The gall provides food for the growing larvae and also protects it. That’s because the developing larvae have lots of enemies, including woodpeckers, mice, parasitic wasps, and other species. Click to learn more about these fascinating galls.

Spiders also leave lots of evidence. Those who weave webs (not all spiders do) leave that very obvious clue to their presence.

Many spiders wrap their eggs in silk, and you might find them suspended within the web. Also look for the insects they have captured for a better idea of what they are eating.

Tarantulas are good to have around because they eat lots of garden pests. But they don’t create webs. Instead, tarantulas live in silk-lined burrows they create as spiderlings and often occupy for the rest of their long lives.

Tarantulas generally hunt at night, so you won’t often come across one unless you accidentally disturb its home. But you may find what looks like a dead tarantula. Chances are that’s only its exuvia—the exoskeleton some animals shed so they can continue to grow. You might also find exuviae of insects such as cicadas and dragonflies.

There are lots of other ways insects and spiders leave clues regarding their existence. You might come across the chrysalis of a metamorphosing butterfly or moth. And you’ve surely seen the nests mud dauber wasps sometimes build on the sides of our homes. We know where spittlebugs are by the bubble homes they create on our plant stems. And that’s just scratching the surface of what you might find. Curious for more? Here’s a book you might like: Tracks and Signs of Insects and Other Invertebrates: A Guide to North American Species by Charley Wiseman and Noah Charney.

How Can We Help?

So what can you do to encourage and protect beneficial insects on your property? Here are a few thoughts from the HELM team:

Avoid Pesticides—Many chemicals, not only insecticides but also fungicides and herbicides, harm pollinators and other beneficial insects and spiders. Even if the tiny creatures aren’t killed outright, exposure can compound the effects of other stressors, such as loss of habitat and exposure to pathogens and diseases. Then there are the impacts on animals higher up in the food chain to consider. So if you do have a problem with an insect pest, first search for an organic solution. Only use pesticides as a last resort and then sparingly and as focused as possible on the problem, sparing the surrounding areas.

Encourage Habitat Diversity—Healthy ecosystems require diversity. A diversity of insects and spiders requires a diversity of plants. At one time cattle and overgrazing had the largest negative impact on the natural diversity of the Texas Hill Country. But today it is deer. Deer density within the Edwards Plateau region increased from an estimated 1.5 million in 2012 to 2.4 million in the 2019 count. So consider creating “deer free” zones, where native plants can thrive and create the diversity our pollinators and other beneficial insects need.

Mow Less—Humans have become a major enemy of plant diversity because invasive plants tend to outcompete desirable native plants when we mow frequently and low to the ground. Think about how much of your property actually needs to be mown, how short, and how often. There are fire-wise reasons for mowing a perimeter around structures. And there might be an area you use for recreation. A few mown paths can enhance your enjoyment of more natural areas of your property. But consider leaving everything else natural—or mown infrequently at times and heights designed to encourage native grasses. And when you do mow, the highest mower setting is best. Now, sit back and think about the work and expense you will save—extra time you will have to simply enjoy your property.

Turn Off/Dim Lights—Nighttime light attracts moths and other nocturnal insects who die prematurely by exhausting themselves circling the light or are easily spotted by predators. Turn off unnecessary lights after dark, and use amber and red bulbs, which are less attractive to insects. Enjoy the reductions in your energy bill.

Learn to Appreciate Bugs—Historically, insects and spiders have been depicted as devourers of crops, disease vectors, hallmarks of poor sanitation, and just general nuisances. But the majority of insects and spiders do not harm humans. And many provide lots of benefits, including controlling the populations of those who might harm us. Rethink your own insect and spider stereotypes and phobias. Learn more about them. An excellent place to start is by identifying them and then learning more about them as a way of understanding their beauty, diversity, and roles in your ecosystem. So next time you are using iNaturalist to identify the spring flowers on your property and spot an insect, spider, or a sign they were there, document it too. Then when you get home, Google to learn more about these tiny creatures who, in the words of E. O. Wilson, “run the world!”