Equine experts in the US are warning horse owners to spray for eastern tent caterpillars as soon as possible. The caterpillars can cause mare reproductive loss syndrome (MRLS), leading to the loss of late-term unborn foals, early-term fetal foals, and weak foals at birth. 
The culprit up close 
The habitat that gives the caterpillar its name 
Snacking on these can be harmful Photos: USFS, USDA/Wikipeida
Eastern tent caterpillars caused the notorious 2001 incident referred to as the Kentucky equine abortion storm, when the state lost around 30% of its thoroughbred foals to MRLS, costing around $336m.
Studies at the University of Kentucky found that mares can inadvertently eat the caterpillars when grazing.
Hairs from the pests embed in the lining of the alimentary tract, allowing bacteria to reproduce in sites with reduced immunity, such as the placenta or developing fetus. MRLS can be confirmed by checking for alimentary tract bacteria.
Lee Townsend of the university recommends that horse farms avoid spraying until the caterpillars are over an inch long. He says: "Foliar sprays for caterpillar control can be made when tents are about the size of a baseball. Another option is injecting trees with a systemic insecticide. Regardless of the treatment used, it is important to revisit the sites in about five days to assess caterpillar activity."
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