Ah, the bounty of spring: all the tender new foliage on trees and shrubs, flowers galore and prolific growth in the vegetable garden.

We gardeners revel in the abundance the season brings, and just like us, insect pests, both big and small, love it, too. Since there are more insects on Earth than all other kinds of creatures combined — more than 900,000 known species — it can be challenging to figure out which ones may be causing problems in your garden. It’s estimated that about 1% of insects are considered harmful, with the vast majority being either neutral or beneficial. By knowing just a few things about these masters of the planet, like their basic anatomy, how they eat and their life cycle, you can quickly narrow down the possible suspects and, if you choose to treat them, develop an effective pest

management strategy. You’re also likely to identify some beneficial insects that you’ll want to keep around.

First, a bit of insect anatomy. All mature insects have three pairs of jointed legs, one pair of antennae, compound eyes and up to two pairs of wings. Spiders and mites are arachnids, not insects. They have two body parts, eight legs, no antennae, simple eyes and no wings. If you observe something crawling around in your blossoms and you count eight legs, it’s not an insect — it’s an arachnid.

Another defining attribute of insects is their mouthparts, the features they use to eat. Insects that cause much of the damage in the garden include those with piercing-sucking mouthparts, rasping-sucking mouthparts and chewing mouthparts.

• Piercing-sucking mouthparts. The outermost layer of plant tissue is pierced, and plant sap from cells is sucked out, which damages the cells and removes valuable nutrients. These types of feeders may excrete a sweet liquid that attracts ants and supports the growth of sooty mold. Plant damage may include distorted leaves, curled leaves, yellowing tissue, deformed fruit and even death of the entire plant. Some insects inject a salivary toxin into the plant that does additional damage. Well-known insects with piercing-sucking mouthparts include aphids, scales, leafhoppers, squash bugs and plant bugs.

• Rasping-sucking mouthparts. The surface of plant tissue is rasped or scraped, and fluids that ooze from the damaged area of tissue are sucked up. Affected tissue dies, turns brown and tears easily; leaves become bleached and dry. The skin of damaged fruit appears sanded, and the underlying tissues may be off-flavored, hard and/or dry. Thrips and mites are common pests with rasping-sucking mouthparts.

• Chewing mouthparts. Plant tissue is bitten, ripped, torn or rasped off. Damage includes holes in leaves, buds, roots, seeds, fruits or woody parts of plants; missing leaves; “windowpane” leaves showing bared veins; and scraped areas. Earwigs, caterpillars, sawfly larvae, webworms, leafrollers, cutworms, flea beetles, blister beetles and cucumber beetles are some of the many insects that feed with chewing mouthparts.

The next important thing to identify is the life stage of the pest that’s doing the damage. The majority of insects undergo some type of change during their lifetime, not only in size but also in form. A simple change has three stages — egg, nymph and adult. Nymphs, the young stage of the insect, look like an adult, only they’re smaller and lack wings. Complete metamorphosis involves a dramatic change (think butterfly). These insects pass through four stages — egg, larva, pupa and adult.

Often, the immature form of an insect is the damaging culprit. These immature stages are highly active feeders and require large amounts of nutrition to support their rapid development. In many cases, the adult does no damage at all, as they’re generally focused on reproduction. Consider the young form of butterflies — the caterpillar may devour lots of foliage, while the adult form lives on pollen and nectar.

Armed with the knowledge of insects’ basic anatomy, feeding habits and life cycles, how many different insects can you find in your garden?

Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provides science- and research-based information for Marin home gardeners. Email questions to helpdesk@marinmg.org. Attach photos for inquiries about plant pests or diseases. Please call 415-473-4910 to see when a master gardener will be at the office or drop off samples 24/7 in the sample box outside the office. To attend a gardening workshop or subscribe to Leaflet, a free quarterly e-newsletter, go to marinmg.ucanr.edu.