A number of animals are often mistaken for pests on farms, nurseries and garden. Most of these are invertebrates that we do not otherwise come across in our day to day lives. Here we identify those animals that are not pests, and in most cases are providing a positive impact on our efforts to grow plants.
Some growers do not appreciate, or are suspicious, of woodlice because they are not entirely sure why they are on crops and what they are doing. Woodlice are crustaceans, which are a form of animal rarely encountered in Britain on terra ferma. The vast majority of crustaceans are detritivores, and woodlice are common in mulch and leaf litter where they break down organic matter into a form that can be used by plants. Only occasionally do woodlice harm cultivated plants, such as eating developing seedlings, but they always prefer dead material if it is available. Woodlice can build up in certain enclosed areas on specific plants, normally to keep themselves moist during the day, as being crustaceans they cannot tolerate dry conditions. One particular site they like is the ears of corn. You might also find woodlice in rotting and half-eaten tomatoes, but this is normally as a result of an initial attack by slugs or blossom end rot. In these cases all the woodlice are doing is eating the decaying plant material and should not be persecuted unjustly. In fact, agricultural ecologists actually determining the population of woodlice in a soil to use as an indicator of its biological health.
These insects are omnivores and, while they do like to take a nibble of tender young shoots of plants, especially on Dahlia, Chrysanthemum, and Clematis plants, they have many benefits to crops. While sometimes viewed as a pest of fruit crops, earwigs have been found to be particularly important for eating aphids and scale insects on fruit trees. As a result, earwigs are now actively encouraged in commercial orchards, with growers attaching ‘earwig hotels’ to apple trees to protect the nocturnal earwigs when the trees are being sprayed with insecticide. In addition, earwigs can also eat dead plant material and so can help cycle nutrients back to plants. We would therefore suggest that if you see earwigs on your plant, have a closer inspection of what they are doing there before you reach for the insecticide.
Centipedes and millepedes
Many growers are also unsure if centipedes and millipedes are beneficial or pests. Centipedes (arthropods belonging to the Chilopoda class) are predominantly carnivores and as such eat other animals living on the crop. Millipedes (arthropods belonging to the Diplopoda class) are both carnivores and detritivores breaking down organic matter in the soil. Therefore, neither centipedes or millipedes are pests.
Definitely one of the least understood groups of animals in soil, and thus we can get confused about what they are and what they are doing. This is often due to springtails being very small and dull-coloured, plus they they live in soil and leaf litter and so keeping themselves to themselves most of the time. Springtails are also confused with fleas because the ones that live in the leaf litter/mulch can jump great distances (relative to their size) if disturbed. This ability is what got them their name.
Further confusing about springtails has arisen because they are not easy to categorise, they are neither insects nor crustacean, and thus placed in their own biological class of ‘Collembola’. Despite us not knowing much about these animals, springtails are actually one of the most abundant animals in the soil and are reputed to even be the most abundant animal on the planet. One estimate puts their populations at 100,000 per cubic metre of topsoil. Further confusion arises because whether they are a pest or not depends on the species. For most growers springtails are beneficial because they break down huge volumes of organic matter and recycling nutrients for plants to use. However, there are some species that eat young roots or tubers, and thus are considered a pest in some agricultural crops.
In hydroponic crops springtail populations can build up to very high levels on the inert growing media. This is normally due to them feeding off the algae and biofilms forming. As such, springtails are helping solve the growers problems, not cause them, so be kind to them!
The larvae of ladybirds look far uglier than the adult form. However, it is actually the larvae that do all the good work for the crop, eating up hundreds of aphids on an infested crop. Despite this, many growers cannot recognise the larvae and might confuse them for a pest. In fact I know of one university professor who mistook them for Colarado Potato Beetles and informed Defra of his shocking find!
They look like ‘aphids on steroids’, but are actually out there eating up hundreds of aphids on your crop. Yes, they might give you a nip on your arm if you get too close but they are most definitely a beneficial animal on your crops!
You might mistake predatory mites for plant-eating (phytophagous) mites such as ‘red spider mites’. However, predatory mites are out there eating spider mites, apple rust mites, aphids, thrips and more! So yes, these mites are most definitely wanted on your crops. Unfortunately, they are far more sensitive to pesticides than plant-eating mites, so be very careful when using miticides and insecticides on your crops.
They are small, black, and to the untrained eye, could be mistaken for a pesky fungus gnat or sciarid fly, specially if you find them on a yellow sticky trap; squished, dehydrated, and dead. However, without question, parasitic wasps are the heroes of the insect world, injecting their eggs into ALL of your pests. That is not even an exaggeration. For every single pest on your crop there is a species of parasitic wasp that will happily kill it. The adult wasp injects her egg into the pests, the larvae hatch and feed off the pest before emerging from its exoskeleton in a process reminiscent of the famous scene from the film ‘Alien’. Not surprisingly, all this results in the death of your plant-eating pests. So please be kind to wasps as well as bees!
Some animals, such as geese, can be a pest in one situation on the farm, and beneficial in others. So it is always worth doing thorough research on the species and their impact before reaching for a control method.
Do you know of any other animals that might be mistaken for pests? If so, please comment below.
Dr Russell Sharp