THUNDER BAY — While many people are used to watching for adult ticks, a local expert said their young can be even more dangerous. Nymphal ticks, or tick nymphs, are the life cycle stage the arachnid goes through before moulting into an adult. Ken Deacon, the coordinator of the Thunder Bay District Health Unit’s vector-borne disease surveillance project, said the black-legged tick nymphs are responsible for most of the transmission of the bacteria that causes Lyme disease. “Probably 60 to 70 per cent of the cases are transmitted by the nymph because people just don’t see them,” he said. “And they’re unaware that they were attached, that the disease was transmitted.” Black-legged ticks, also known as deer ticks, are responsible for Lyme disease, while wood ticks don’t carry the bacteria. While a fully-engorged adult female black-legged tick can be larger than the size of a pea, Deacon said, by comparison, the nymph is smaller than a sesame seed.