Plant Pests: Tiny White Worm-Like Insects

Type

• Many whitish, wormlike pests visiting your ornamental plants, vegetable garden or even houseplants are the immature stages of flies, moths or beetles. Fly larvae are called maggots, moth larvae are called caterpillars and beetle larvae are most often called grubs. All have a similar body shape: long, cylindrical and vaguely resembling worms. Grubs and maggots often have a distinct head that is usually darker than the body, and grubs often have three distinct legs near their head. Caterpillars often have many leglike appendages.

Size

• Even if you've concluded the culprits are tiny, a more exact size can help you better identify what is chewing on your favored plants. Among the simplest methods of determining exact size is to take a specimen and hold it against a ruler. If it's particularly small, use a ruler with millimeter or centimeter marks. Root maggots and asparagus beetle larvae grow up to 1/4 inch long, and fruitworms can grow up to 1/2 inch long. Fungus gnat larvae are particularly small, sometimes much less than 1/4 inch long.

Host Plant or Location

• The location of the pest can also help in identification. Most larvae and wormlike pests have one or a couple of specific plant hosts, meaning they only feed on their hosts. Asparagus beetle larvae, for example, prefer to feed on the ferns and berries of asparagus (Asparagus officinalis) plants, which grow in U.S. Department of Agriculture plant hardiness zones 4 through 8. Onion and cabbage root maggots feed on the roots of their namesakes, along with several other cruciferous (Brassica spp.) plants. Codling moth larvae burrow into apples (Malus domestica and cvs.), which typically grow well in USDA zones 5 through 7, although low-chill and cold-hardy varieties exist; into crabapples (Malus spp.), which are hardy in USDA zones 4 through 8, and into pears (Pyrus spp.), most of which grow in USDA zones 5 through 8. European corn borers prefer annual corn (Zea mays), peppers (Capsicum spp.) and Irish potatoes (Solanum tubersom). Fungus gnat and shore fly larvae are clear to white and often feed on fungi, organic material in soil or algae in greenhouse or container plants.

Damage

• The damage symptoms on the plants can also help you determine which creature is inhabiting your garden. Some wormlike pests feed on foliage, whereas others attack the roots or fruit of your favorite plants. Various leafminers, for example, leave distinctive marks in the tops of leaves. Pickleworms begin feeding on cucurbit foliage and later the fruit. The 1/4-inch-long raspberry fruitworm larvae feed on immature berries.