I have lived close to Wareham Common for fourteen years and so visit quite regularly and I have become increasingly concerned at the dearth of invertebrate species in recent years. There has, as is well known, been a general decline in insect populations linked primarily to neonicotinoid pesticides but on the common, and also at Stonehill Down recently where there are a significant number of cattle grazed, I have noticed a change in cattle excrement.
I am venturing into the realms of veterinary science here which I am reluctant to do with no background in this particular field but it seems that cattle are now fed a routine medication called ivermectin to combat certain gut infections. I found a little bit about Ivermectin on the 'net':
"Studies indicate that when ivermectin comes into contract with the soil it readily and tightly binds to the soil and becomes inactive over time. Free ivermectin may adversely affect fish and certain water-borne organisms on which they feed. Do not permit runoff from feedlots or production sites to enter streams, lakes or ponds."
Whilst this text is not directly related to invertebrate life on grassland this must surely have an effect on insect life where substantial cattle dung accumulates?
I have no idea if the cattle on the common are receiving this treatment but one thing I have noticed since this practice came into being around five years ago is that the good old fashioned ‘country pancake’ we were familiar with has all but gone. Cow excrement is now slimy and smeared across the grass and can be unpleasant to negotiate on foot.
That is not my main concern however. Once, when a new ‘pancake’ was deposited, an abundance of flies, yellow dung fly and greenbottle in particular, and species of scarab beetles would descend on it to lay eggs. Their eggs then hatched into larvae which ate the cow pat thus naturally biodegrading it. It seems nothing can deal with the new form of excrement partly because it contains this pesticide that kills the freshly laid eggs and/or larvae.
The flies that used cow pats had benefits to human beings and the environment in general other than just decomposing and freeing us from cow dung, they contributed to the pollination of some plants and are food for some other animals, mainly birds. Yellow dung flies were once abundant but are now very scarce on the common and so other species must surely be affected too?
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