ADVANCES
20 Scientific American, March 2022
BIOMECHANICSScience
in Images
By Gary Hartley
To wrangle a ride on their honeybee hosts, wing-
less parasitic flies need a truly phenomenal grasp.
Now a new study reveals how Braula coeca manages
to walk around on a flying bee while exhibiting what
researchers say is the highest attachment force per
body weight of any land-based insect ever measured.
This force relies on the parasite’s highly adapted
feet, called tarsi, which are equipped with toothed
claws. Each foot has a total of 28 teeth, or claw tips,
which let the parasite lock onto sparse honeybee
hairs during flight.
“The claws are unique, from what we know so
far. Usually insects have claws with one tip only.
A few species have two to three tips. But this species
possesses comblike claws with several tips and deep
interstices [gaps],” says Thies Büscher, a zoologist
at Germany’s Kiel University and co-lead author
of a recent study in Physiological Entomology.
The claws are complemented by soft lateral
ridges and “stoppers” along the foot, letting the fly
swiftly break its rigid grip with a simple twisting
motion and detach from the hairs as it moves—
a trait likely to be intriguing to researchers working
in biology-influenced design, or biomimetics. The
parasite’s feet also feature pads that firmly cling to
smooth surfaces, such as the wax in beehives.
“Other strongly attaching animals either secrete
strong glues or anchor with structures that damage
the surface,” Büscher says. “Both solutions are more
or less permanent and do not allow for fast detach-
ment and locomotion.” But because B. coeca’ s
grasping mechanisms are purely mechanical, they
could prove useful for both terrestrial and under-
water robots.
“Attachment technology is a prominent domain
within biomimetic research,” says Shoshanah Jacobs,
an integrative biologist at the University of Guelph in
Ontario, who was not involved in the research.
Jacobs agrees with Büscher on the finding’s potential
value but notes that designers working on attach-
ment problems might not readily become aware
of such discoveries in insect physiology.
“Biomimetic researchers grapple with the chal-
lenges of knowledge mobilization across disciplin-
ary silos,” Jacobs says. “When we’ve figured out
how to do this better, we may very well be opening
a floodgate of innovation.”
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