Unfortunately the useful boarders, who pay for their keep in my glasshouse, are greatly outnumbered by the free-loading squatters. Probably the most useful boarder is the tiny jumping spider. These comical creatures, with their huge eye-patches and the ability to jump many times their body length, probably eat their weight in ‘squatters’ every week. I have mixed feelings about fungus gnats, those small winged insects that creep over bark-based potting mixes, because I don’t know their diet. If they prey on Phytophthora and other pathogenic fungi; then I’m all for them. But if their main diet consists of the mycorrhizal fungi that provide food for developing orchids, then maybe they should be regarded as squatters. Predatory mites, whose sole diet is the two-spotted mite (red spider), are definitely top-class boarders.
Some growers encourage small frogs that prey on a variety of insect pests but small frogs that grow into big frogs topple pots and sometimes break flower spikes during their amorous adventures after dark. Ladybirds are highly regarded for their ability to eat large numbers of aphids. Unfortunately, my orchids seem to attract many aphids but few ladybirds.
Long experience has made me an expert when it comes to squatters in the glasshouse. Slugs and snails are undoubtedly the worst. In the garden they’re mainly a pest after rain but in the glasshouse snails and slugs are continually active, because the floor is always wet. Theoretically my plants should be safe because they are grown on benches constructed of galvanised iron (snails and slugs dislike crawling on zinc-coated surfaces). However, the cunning devils use weeds, ferns and 1mpatiens (a colourful glasshouse weed) as step-ladders to reach the orchids. The solution is to remove the weeds and to regularly sprinkle snail bait (Baysol® or Defender®) where our pets cannot reach. Please note that all products listed in this article are toxic and that they should therefore be handled with appropriate safety precautions.
Garlic snails, so-called because of their smell when crushed, are another menace. They feed largely on active root tips and probably retard the growth of small seedlings, in particular, much more than we realise. During the day they hide but they can easily be seen at night when they come out to forage. They are quite small, about the size of an ‘0’ on this page, even when fully grown. Liquid snail baits containing Methiocarb® offer better control than do solid baits. Caterpillars of various sorts can do much damage in a short time, as they invariably attack the fresh, new growths. Dusts based on carbaryl or derris root work well on most but not on those little fellows that sew themselves inside the growing leaf tip. One can use systemic insecticides, but I usually extract these caterpillars by hand and finish them off by foot!
Aphid outbreaks seem to occur regularly in my collection. Some cymbidium growers blast them off the flower buds, where they largely congregate, with a jet of water from the hose. The trick is to use enough force to dislodge the aphids without simultaneously removing the buds! This technique is unsuitable for use on the smaller plants in the glasshouse. Many insect sprays are effective but some result in distorted flowers when applied to orchids in bud. I use a wettable powder called Orthene®, which does not affect buds or flowers. Unfortunately it is available only in large, wholesale quantities and has a most objectionable odour in powder form; fortunately, it’s less unpleasant when dissolved in water for application.
Unfortunately, the greatest free-loader of them all, our black cat, Max, is no longer with us. However, on the basis of past experience, I strongly advise you never to lock a hungry, mentally unstable cat accidentally (or deliberately) in your glasshouse overnight!