What makes a tick-host encounter successful? Isolating the effects of host and tick qualities on rates of larvae adhering to hosts

Blacklegged ticks (Ixodes scapularis) require a single bloodmeal from one
of many potential host species during each of their three life stages.
However, host species vary tremendously in their permissiveness for ticks.
Given the variation in tick survival on hosts, we would expect ticks to
have evolved mechanisms that increase their probability of feeding on
highly permissive species. However, we know little of what happens during
an encounter between a tick and a passing host. To explore the influence
of host and tick qualities on the probability ticks adhere to hosts, we
constructed an apparatus in which an artificial host passed over I.
scapularis larvae, simulating hosts walking over ticks. This allowed us to
control isolated qualities of the host and ticks we hypothesized to be
important and observe how many larvae adhered to hosts. In one experiment,
larvae were twice as likely to adhere to mouse fur than opossum fur, and
even less likely to adhere to drag cloth corduroy. However, fur type had
no apparent effect in a second study. Instead, the probability larvae
adhered to a host increased rapidly with the duration of contact,
saturating by ~1 s regardless of fur type, and slightly influenced by host
speed. Even with the longest contact times only ~2/3 of larvae adhered to
a host. This probability declined with larval age. Collectively, our
results suggest ticks may attempt to adhere to any host they contact,
perhaps because contacts are rare and often brief, but not all
host-seeking ticks are in a state where they can or will adhere.