Any serious wildlife conservationist, rancher or hunter is aware of the deadly EHD (epizootic hemorrhagic disease) affecting primarily whitetail deer, as well as elk, pronghorn antelope and other ruminants across the country. A related disease, known as bluetongue, is more common in domestic sheep, cattle, and goats, though occasionally is found in whitetail deer and other wild ruminants. Both types of disease can be a significant concern for owners and managers of hunting parcels. There is no treatment for HD in wildlife populations where mortality rates can be as high as 90%.
Outbreaks of EHD tend to be highly localized, since the disease is spread by biting midges, also known as gnats or “no-see-ums,” which congregate closely around individual watering holes. Wind can carry infected midges to new locations, however, leading to sudden unexpected outbreaks.
EHD tends to spike during periods of drought, which is a particular concern for land stewards seeking to improve their parcels, since that’s when deer will be most attracted to managed water holes.
Since no treatment is available for wild deer populations, the only sensible response is prevention. Let’s discuss some strategies that can minimize midge populations and reduce exposure for deer on your land.
Breeding Grounds
Midges congregate near water holes and deer ponds because that’s where they breed and in areas where water is scarce, their food sources (deer) courteously stop by daily for another meal. Preventing deer from visiting water sources obviously isn’t a viable option, so it’s up to you to control their opportunities to breed.
Midges prefer shallow, murky, warm water with a muddy or silty bank that’s frequently disturbed by large animals like deer, cattle, or feral hogs. Disturbed margins stir up mud and silt which keeps the water murky and protects larvae from natural predation. Ponds with shallow margins exposed to direct sunlight will be warm even when the air is relatively cool. When you assess the condition of your pond, keep an eye out for an excess of mosquitoes, since they’re also drawn to low-quality water.
In addition to establishing conditions that are unfavorable to midge breeding, consider establishing several smaller hunting ponds distributed across your tract, perhaps leading to separate feed lots. Multiple water sources encourage your deer population to spread out, so even if one pond is infested with disease-carrying midges, you’re unlikely to see a catastrophic die-off. This reduces individual risk but also gives the deer some options, since they’ll try to avoid water sources with large swarms of biting insects.
When you’re choosing a site and designing your pond, keep midge control in mind. Shady ponds are unattractive to midges since they tend to be cooler, while ponds with steeper profiles don’t offer the shallow water that midges prefer. Avoid extremely dark locations though, because you’ll also want to encourage protective plants to get established.
Water Quality
Midges prefer sites where water quality tends to be low. Turbid water offers good camouflage, while highly mineralized water is detrimental to predators like dragonflies. High levels of nutrients trigger algae blooms, which can damage natural predator populations.
In an earlier article, we discussed algae control and the problems associated with nutrients in runoff. Excessive nutrients cause problems in all aspects of pond management, so it’s important to keep that under control. In addition, consider the level of minerals in your pond. Salt and mineral licks placed near a deer pond allow rain to dissolve and carry minerals into your pond, and high levels of mineral supplements added directly to the water can exacerbate the issue. A layer of soil at the bottom of your pond will provide enough minerals to appeal to deer, while locating licks downgrade of your hunting pond will prevent incursion from these sources.
If you’re dealing with problems in a single large pond, you may find a higher level of intervention worthwhile. One effective option involves moving water. Biting insects like midges and mosquitoes prefer still water for laying eggs. In a deer pond or small watering hole, water movement can be provided with a pump or aerator. Obviously, most ponds in a hunting reserve aren’t going to be near an electric grid, but there are plenty of options for even small-scale solar and windmill power. It’s not necessary to install a fountain or high powered pump - a pond pump that creates moderate movement along the margins of the pond will encourage midges to search out a more suitable location.
Focus on the Banks
We’ve discussed strategies for maintaining clear, deep, cool bodies of water where midges prefer not to breed. Midges also avoid vegetated or rocky banks where mud is at a minimum. Biting midge species spend much of their larval stages in churned up mud around waterholes where they consume decaying organic matter, so eliminating access to those food sources is a key goal.
To control midges, model your hunting pond after healthy ponds surrounded by native plants that extend all the way to the water’s edge and absolutely avoid mud holes surrounded by churned up soil. You can add rocks to protect parts of the margin, which can be especially helpful where runoff enters the pond. A mix of large rocks and gravel will slow down incoming water, help protect from erosion, and prevent a buildup of surface mud. Relatively steep sides will also help - an abrupt drop off, of even 6 inches makes the pond unsuitable for midge breeding.
If you use large rocks to line the margins of your pond, be sure to allow several points of easy access for deer. To minimize mud at these access points, vegetation is your best defense. We discussed marginal plantings such as duck potato in a previous article on algae control, and those same plants will do double duty in midge control. Native sedges and rushes are another great option; they provide excellent cover, habitat for beneficial insects like dragonflies, and eliminate the mud that midges love by securing wet soil with closely woven roots. They take up excess nutrients and capture sediment, improving water quality and reducing the presence of algae. Marginal plants mitigate problems with erosion and sediment, and some may be an extra food source for deer. In fact, vegetated margins in deer ponds offer such an important range of benefits that they represent some of the most important (and least expensive) features you can add.
Natural Predators
In general, midge larvae are vulnerable to predation by fish, dragonfly larvae, water beetles, and other insects, although predators specific to Culicoides midges haven’t been widely studied. Still, it’s a good strategy to encourage dragonflies, water beetles and other insects to take up residence whenever possible.
Adult midges are a favorite food source for swallows, spiders, bats, and predatory aquatic insects. Consider establishing some nesting sites for insect loving birds and bats near your watering holes; a variety of suitable birdhouse plans are available on the internet. Keep in mind that midges are most active at dawn and dusk, which is perfect for bats. Do some research to discover which insect-loving birds in your area tend to hunt at those times so you can attract the most effective population controls.
