Issue: March 16, 1998

Pine aphids

I have little ugly spiders in my pine tree. They are baby spiders with long legs and group together in bunches on the twigs. What kind of spider is it and what can I do? Are they dangerous?

The samples you sent are not spiders - they are aphids with long legs. These aphids are a type of aphid which infests pine trees and causes some problems.

First, if you wish to investigate and look at the aphids in the tree, be sure to wear safety glasses. A few years ago I spoke to a gentleman who, when looking closely at these aphids, forgot that pine needles have a sharp point. He pierced his eye with the pine needle. Fortunately, beyond the pain and a period of healing, he had no permanent damage to his eye.

The aphids feed by piercing the stem of the pine with a stylet mouthpart. This is then used like a soda straw to draw "sap" and nutrients from the plant. As the sap has an excess of sugar from the aphids' perspective, they excrete a sugary syrup, called honeydew. This is the mist of droplets that make windshields of cars sticky and create a problem for car paint. You may notice "wet" patches on sidewalks under pine trees where this syrup accumulates. Besides being a nuisance for owners of cars parked under pines or people sitting on chairs or benches under the trees, the aphids are robbing the trees of the sugars and amino acids that they have synthesized from sunlight, water, and carbon dioxide. These materials were made to feed the tree, not the aphids. So, the trees are injured as they have lost some of their food supply. As this honeydew accumulates on the leaves and twigs of the tree, a fungus, sooty mold, begins to grow, using the honeydew as a food. The sooty mold doesn't hurt the tree except when heavy amounts develop and block sunlight from the chlorophyll of the leaves. In this instance, the sooty mold can then reduce photosynthesis and the ability of the tree to synthesize the food it needs.

Now regarding your question, "Are they dangerous?" - the answer is that they are not particularly dangerous. Of course a messed up windshield on a car can cause traffic dangers, but the aphids do not injure people, only plants. The next question to ask is should you do anything about the aphids. The answer is one you must answer for yourself. If you see great numbers of aphids on many of the twigs in the tree, you may choose to treat to reduce the aphid population and limit the damage to the trees. If the honeydew is causing problems, you may also choose to treat. However, if you find numerous lady bird beetles or lacewing larvae in the tree, you should allow the natural controls, these insect predators of aphids, to do the job.

If you decide to treat, you may use a strong jet of water to wash many of the aphids from the twigs if the infested branches are within range of a strong stream of water from the garden hose. You may also use one of the insecticide products available at your local garden store. Be sure to select a product labeled for control of aphids on the pine or other trees you have found infested. Read and carefully follow the directions on the label when applying any pesticide, even "organic" or natural pest control products.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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