Dear Miss Floribunda,
A couple of months ago, my holly was covered with spider webs (see picture) and some of the leaves had yellow spots on them and fell off. This has happened in the past, and I used insecticidal soap on them, but I’ve come to understand how bad poisons are, so this year I just hosed them very vigorously and threw away the dead leaves. This seemed to work and they seem OK, but now my roses and other plants have the same webbing.
Can you tell from the webbing what the spider might be and what to do about it? I don’t like to spray my roses with water because that encourages black spot. Also, do you suppose the spider might be harmful to people? I haven’t seen it yet and, frankly, I’m afraid to.
Webbed on Webster Street
I consulted my expert in arachnology, Dr. Arthur O. Podd, and his first reaction to the photo I showed him was to reproach me for not knowing that spiders spin beautiful webs like fine lace: “This mess is the work of spider mites.” He pointed out that spiders are beneficial in the garden, reducing the number of such harmful insects as mosquitoes, thrips, midges — and, yes, spider mites. On the other hand, the mites do nothing but suck the life out of your plants. He believes that what you have is the southern red spider mite, which is partial to holly. You would notice a real spider, but mites are so tiny you need a magnifying glass to see them. The yellow spots on the leaves were a giveaway, though.
Spider mites are indeed related to spiders, as well as to ticks, chiggers, scorpions and solifugae. They are in the same genetic class, the arachnids, but are in the acari suborder along with ticks. Though creepy and crawly, arachnids differ from insects in many respects. Most notably, they have eight rather than six legs; they have neither wings nor antennae; and their bodies comprise two rather than three parts. This family was named after Arachne, a character in Greek mythology who challenged the goddess Athena to a weaving contest. Although technically Arachne won, her reward was to be turned into a spider.
Now, how did this horror come upon you and what can you do about it? The insecticidal soap probably just killed insects, leaving the field clear for more mites. Hosing the holly leaves was indeed the best thing you could have done. Not only did it clear away the mites and their webbing but it watered the holly. Dryness encourages mites, who usually attack during the dry dog days of summer, but this year we had an oddly dry April. Spider mites look for moisture and find it in the sap of plants. They are a well-known bane of houseplants in the hot, dry environment that prevails indoors during winter.
You are right that hosing your roses would encourage black spot. Instead, prune off the affected areas and dispose of them without composting. Keep your rose bushes deeply watered. A hollow PVC pipe pounded a foot into the ground next to each bush allows you to put in the hose nozzle and water till the roots are reached. Do this weekly in the absence of a good rain. You don’t need to get any water on the leaves of the bushes. By the way, if your rosebushes are as closely spaced as your holly bushes are, this might also encourage infestation. During winter dormancy, you might want to dig up some of your holly and roses and space them farther apart. Also, when cool weather comes, you could spray them with horticultural oil to kill any eggs that might overwinter. Please don’t do it now. To use oil on plants in hot weather is tantamount to frying or boiling them in the kitchen.
About the danger of spiders, there are only two in our area that are seriously poisonous, but they are very shy and avoid people. The brown recluse, as its name implies, is not likely to come looking for you. The black widow is the other potentially dangerous spider, and even this one is not as evil as its legend. It won’t bite unless it feels threatened and can even reduce or increase the level of venom according to the level of perceived threat. The female very rarely consumes her mate, who apparently knows just what little dance to perform. (One can only speculate on what he promises or what flattery he communicates with this dance. The rare fatalities are the less adroit perhaps, those who don’t know how to respond when asked, “Do I look fat in this web?”) The only black widow spider “attacks” I’ve heard of are from western black widows inadvertently caught in bags of grapes from the supermarket. A spider surprised by a big hand seemingly coming out of nowhere would feel attacked. You will not be attacked in the garden even if a spider should use you as a short cut. I know very well how startling this can be but can testify it’s not dangerous.
The Hyattsville Horticultural Society usually meets on the third Saturday of each month but on July 15 will instead visit the Lotus and Water Lily Festival at the Kenilworth Aquatic Gardens. The entrance is at 1550 Anacostia Avenue, NE. The gardens open at 8 a.m. and close at 4 p.m.