A Fact Sheet Series on Managing Lands for Wildlife
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Habitats A Fact Sheet Series on Managing Lands for Wildlife Beneficial Insects and Spiders in Your Maine Backyard Bulletin #7150 nsects, spiders, predatory mites, and other not killing them outright. While predators attack arthropods are considered beneficial when many pests to complete development, parasitoids they eat arthropods that humans consider kill only one or a few pests each. undesirable. Few arthropods are actually pests; of all insect species, over 97 percent Of all insect species, over 97 percent Iof those usually seen in the home landscape are either beneficial or are “innocent bystanders.” of those usually seen in the home Managing our yards as habitat for beneficial arthropods—commonly called “natural enemies” landscape are either beneficial or are or “beneficials”—is a great way to minimize pest “innocent bystanders.” problems, often greatly reducing or eliminating pesticides. This fact sheet describes a long-term, systems-wide approach to manage arthropod pests. A Top Eleven List of Beneficial Predators and Parasitoids Insects and Spiders There are two categories of beneficial arthropods: Spiders predators and parasitoids. Both can effectively Description: Spiders have no control insect and mite pests in your home landscape. antennae and two body parts: Predators are organisms that kill and feed on the cephalothorax, containing prey. They are generally larger than their prey. the eight legs, eyes and Parasitoids, on the other hand, are typically smaller mouth; and the abdomen, than their hosts and lay eggs on or within them. containing the digestive organs, genitals and When the eggs hatch into larvae, these larvae spinnerets. Spiders are an incredibly diverse develop and feed on these host insects, causing group with roughly 3,000 described species in their death. In some cases, adult parasitoids will North America. While most have venom glands act like predators by feeding on the blood of host of some kind, spiders rarely bite people. Brown insects without laying eggs, weakening them if recluse and black widow spiders are not normally found in Maine. Value in the home landscape and garden: All spiders are predators, and most feed on insects caught in a web. Others, such as jumping spiders and wolf spiders, are active hunters relying on excellent vision to kill their prey. Crab spiders, another commonly encountered group, ambush LADYBEETLE, ADULT PUPA LARVA their prey. A recent study1 indicates that spiders are often the most abundant predators, as a Lady beetles group, on a wide range of plant material in the Description: Most people recognize the dome- home landscape. shaped, often brightly colored adults, also known as “ladybugs” and ladybird beetles, that range in Green and brown size from one-sixteenth to three-eighths of an inch lacewings long. Colors are highly variable and include Description: Lacewings lay orange, black, pink or yellow. Spots may or may GREEN their eggs at the end of long not be present. LACEWING, ADULT AND stalks, presumably to protect The adult female beetle lays groups of 10–50 EGGS them from ants and other orange, football-shaped eggs, usually on upper lacewing larvae. The larvae of both green and leaf surfaces or twigs. The eggs hatch into spiny, brown lacewings are alligator-like with sickle- black and orange, alligator-like larvae. Some lady shaped mandibles. Adult green lacewings are beetle larvae that feed on mealybugs have a white, approximately three-quarters of an inch long and waxy covering (similar to that of mealybugs). pale green, with large copper-colored eyes. They After feeding, the larvae pupate, usually on the are attracted to lights at night, and can produce a underside of the leaf near their prey, and emerge noxious odor when handled. Brown lacewing as adults. Lady beetles spend the winter as adults adults are tan or brown and about half the size of in protected areas and can live for 11 months or green lacewing adults. longer, some as long as two to three years. Value in the home landscape and garden: Green The multi-colored lady beetle (Harmonia lacewing larvae are called “aphid lions” for good axyridis), also known as the Halloween lady reason; they attack and consume large numbers of beetle, while beneficial, often enters homes in aphids, mites, lace bugs and other small insects. large numbers. You can prevent their entry by Pollen, nectar and even honeydew sustain the carefully examining the exterior of the house, generally nonpredaceous adults. Green lacewing sealing cracks and crevices, and screening vents larvae can be purchased commercially and offer a using 20 mesh screen or smaller. safe, though sometimes costly, nonchemical One of the few pests in this group is the alternative for controlling aphids and lace bugs. Mexican bean beetle (Epilachna varivestis), which in its adult stage is yellow with 16 black spots on its wing covers. 1 Colin Stewart, S. Kristine Braman, and Beverly Sparks, “Abundance of Beneficial Arthropods on Woody Landscape Value in the home landscape and garden: Both Plants at Commercially-Managed Landscape Sites,” Journal the larvae and adult lady beetles are voracious of Environmental Horticulture v20 n2 (2002): 67-72. 2 HABITATS: A FACT SHEET SERIES ON MANAGING LANDS FOR WILDLIFE predators that can eat hundreds of aphids in their and scale insects. Dustywings have been described lifetime. They also eat insect eggs, mealybugs, as one of the most under-appreciated and and other soft-bodied insects and mites. Some unrecognized predators in the landscape. While species of lady beetles have favorite prey, as this insect is said to be uncommon, one of the indicated by the names given to the “mealybug authors of this fact sheet, Colin Stewart, has destroyer” and the “spider mite destroyer.” encountered many of them in Maine, Pennsylvania Flowering, pollen-producing plants in the and Georgia. landscape attract lady beetles. Praying mantids Ground beetles Description: This large, Description: Most of these highly distinctive insect is are shiny brown, black, or tan, green, or gray, may be blue-black insects ranging in up to three inches long, and PRAYING MANTID size from one quarter to over has large, bulging eyes on GROUND BEETLE one inch long, with long legs the sides of its head. A distinctive feature is its and long antennae. Most ground beetles are enlarged first pair of legs, which are held out in nocturnal and have prominent jaws used to kill front of its body as though it were praying. There caterpillars (including armyworms, cutworms, and is one generation per year. Females deposit a tan, grubs) and other insects, as well as small snails bubbly egg mass on branches near the end of the and slugs. Both adults and larvae are predators. summer. The egg mass, which hardens, contains One species, Calosoma sycophanta, is a climber. over 200 eggs. Value in the home landscape and garden: One Value in the home landscape and garden: Calosoma sycophanta larva can consume 50 large Because these insects feed on anything they can gypsy moth caterpillars in two weeks, while a catch, including honey bees, each other, and other pair of adults can devour over 300 gypsy moth beneficial insects, their value in reducing the caterpillars and pupae per year. Ground beetles numbers of key pests in the garden and landscape typically have one generation per year, and some is questionable. Contrary to popular belief, they adults can live for two to four years. are not protected by any state or federal laws. Dustywings Hover flies (syrphid Description: Dustywing flies or flower flies) larvae are often mistaken for Description: These nonbiting plant debris. Adults are a and nonstinging flies closely quarter of an inch long or DUSTYWING resemble wasps and bees, in less, with gray, dusty wings. FLOWER FLY that they usually have a There are two generations per year and the yellow abdomen encircled by brown or black insects overwinter as larvae. stripes. Adults are typically one-half to three- Value in the home landscape and garden: Both quarters of an inch long. Unlike bees and wasps, larvae and adults feed on spider mites, aphids, these insects have only two wings. The legless BENEFICIAL INSECTS AND SPIDERS IN YOUR MAINE BACKYARD, BULLETIN #7150 3 Attracting and Sustaining larvae, sometimes mistaken for tiny slugs, are “Good Bugs” pale green, clear, or yellow and are usually found Develop a tolerance for some damage by in the midst of aphid colonies. The larvae also arthropods to your plants; many plants can tolerate deposit tar-like excrement around the feeding site. low levels of pest damage with few ill effects. Value in the home landscape and garden: The Provide shelter. Leaving some leaf litter and debris under shrubs may provide beneficial larvae are valuable aphid and adelgid predators, arthropods a place to hide during adverse capable of consuming over 400 aphids before conditions such as hot summer days. pupating. Providing food for the nectar- and Increase the diversity of your landscape. pollen-feeding adults by planting flowers will Grow a wide assortment of plants to create encourage them to lay eggs in the landscape or habitat for a wide range of natural enemies. Also, garden. Hover flies are excellent at detecting and diverse plantings of the right species that are pest and disease resistant make it less likely that attacking even low numbers of aphids. pests will cause problems. Do not use zapper lights that electrocute Predatory bugs insects. In study at the University of Delaware, These predatory bugs also feed on nectar and pollen. these lights killed many more beneficial insects Big-eyed bugs are aptly than pests. named insects that are about Ensure a continuous supply of floral nectar one-eighth inch long, black and pollen by selecting plants with a and white, with silvery succession of flowering times.