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R.J. thanks the Air Force Office of Scientific Research [award
no. FA9550-15-1-9999 (FA9550-15-1-0154)] and the Camille
Dreyfus Teacher-Scholar Awards Program for financial support. All
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Materials and Methods
Figs. S1 to S11
Tables S1 and S2
22 September 2016; accepted 16 November 2016
Mass seasonal bioflows of high-flying
Gao Hu,1,2,3 Ka S. Lim,2 Nir Horvitz,4 Suzanne J. Clark,2 Don R. Reynolds,5
Nir Sapir,6 Jason W. Chapman2,3*
Migrating animals have an impact on ecosystems directly via influxes of predators, prey,
and competitors and indirectly by vectoring nutrients, energy, and pathogens. Although
linkages between vertebrate movements and ecosystem processes have been established,
the effects of mass insect “bioflows” have not been described. We quantified biomass
flux over the southern United Kingdom for high-flying (>150 meters) insects and show that
~3.5 trillion insects (3200 tons of biomass) migrate above the region annually. These flows
are not randomly directed in insects larger than 10 milligrams, which exploit seasonally
beneficial tailwinds. Large seasonal differences in the southward versus northward transfer
of biomass occur in some years, although flows were balanced over the 10-year period. Our
long-term study reveals a major transport process with implications for ecosystem
services, processes, and biogeochemistry.
Latitudinal migrations of vast numbers of lying insects, birds, and bats (1–7) lead to huge seasonal exchanges of biomass and nutrients across the Earth’s surface (8–11). Because many migrant species (particularly
insects) are extremely abundant (1, 5), seasonal
migrations may profoundly affect communities
through predation and competition while transferring enormous quantities of energy, nutrients,
propagules, pathogens, and parasites between
regions, with substantial effects on essential ecosystem services, processes, and biogeochemistry
(8–11), and, ultimately, ecosystem function.
Latitudinal bird migrations are well charac-
terized; for example, 2.1 billion passerines migrate
annually between Europe and Africa (2), inte-
grating multisensory navigational information (12),
exploiting favorable winds and adopting adaptive
flight behaviors (13). By comparison, even though
insect migration surpasses all other aerial migra-
tory phenomena in terms of sheer abundance (1),
latitudinal insect migration is largely unquan-
tified, in particular for the majority of species that
migrate hundreds of meters above the ground (5).
Specialized radar techniques are required to study
these high-flying insect migrants, as they are too
small to carry transmitters or to be observed by
any other means (14). Until now, radar studies
have been aimed almost exclusively at quantifying
migrations of relatively few nocturnal species of
agricultural pests (3).
We quantified annual abundance and biomass
of three size categories of diurnal and nocturnal
insects migrating above an area of ~70,000 km2
of the southern United Kingdom (Fig. 1A), be-
tween 150 and 1200 m above ground level (agl)
(Fig. 1B), from 2000 to 2009 (15). Abundance and
biomass values for medium (10 to 70 mg) and
large insects (70 to 500 mg) (referred to collect-
ively as “larger insects”) were calculated from
measurements of >1.8 million individuals (table
S1) detected by vertical-looking entomological
radars (VLRs) located in the southern United
Kingdom (Fig. 1A). The VLRs provide a range of
information—including body mass, flight altitude,
aerial density, displacement speed, displacement
direction, and flight heading—for all individual
insects of >10-mg body mass that fly through the
vertically pointing beam within the altitude range
of 150 to 1200 m agl (14). Annual abundance and
biomass values for larger insects migrating over
the study area were extrapolated from the aerial
densities and body masses recorded above the
VLR locations (15). The third size category, small
insects (<10 mg), are not sampled by VLRs, and
so abundance and biomass data were calculated
from aerial netting samples (16) taken ~200 m
agl near one of the radars (Fig. 1A) and extra-
polated to the study area (15). Larger diurnal
migrants are predominantly beneficial species,
including hoverflies, ladybeetles, carabid beetles,
and butterflies (14–17), and the most abundant
small day-fliers are cereal aphids (16). The com-
monest larger nocturnal insects are lacewings
and noctuid moths (14, 16), whereas Diptera con-
stitute the majority of the small nocturnal insects (16).
An annual mean of 3.37 trillion insects (range
1.92 to 5.01 × 1012) (Fig. 1C and table S2) migrated
high above the study region, comprising 3200
tons of biomass (fig. S1 and table S3), and >70%
of that biomass was from migration that oc-
curred during daytime (Fig. 1C and table S2).
Numerically, >99% of individuals were small in-
sects; although the 15 billion medium and 1.5 billion
large insects made up only 0.4% and 0.05% of
the annual abundance (table S2), they accounted
for a substantial proportion of the biomass: 12%
(380 tons) and 7% (225 tons), respectively (table S3).
By analyzing 1320 daytime “mass migrations”
(15) involving 1.25 million VLR-detected insects
and 898 nocturnal mass migrations involving
126,000 insects (table S1), we characterized migration directions of the larger insects during
“spring” (May to June), “summer” (July) and “fall”
(August to September) (fig. S2 and table S4).
Although high-altitude winds blew consistently
toward the northeast or east in all three seasons
(Rayleigh tests; daytime: spring, 60°; summer,
66°; fall, 84°; nighttime: spring, 69°; summer, 81°;
fall, 101°) (Fig. 2A and table S5), mass migrations
of larger insects did not simply move with the
prevailing southwesterly winds. During the spring,
mass migrations were consistently toward the
north (Rayleigh tests; daytime: medium, 333°;
large, 329°; nighttime: medium, 349°; large, 349°)
(Fig. 2A), and this indicates that migration occurred on winds with a significantly more southerly component than prevailing winds (
Watson-Wheeler tests; P < 0.0001 in all cases) (table S5).
1584 23 DECEMBER 2016 • VOL 354 ISSUE 6319 sciencemag.org SCIENCE
1College of Plant Protection, Nanjing Agricultural University,
Nanjing, China. 2Rothamsted Research, Harpenden,
Hertfordshire, UK. 3Centre for Ecology and Conservation, and
Environment and Sustainability Institute, University of Exeter,
Penryn, Cornwall, UK. 4Movement Ecology Laboratory,
Department of Ecology, Evolution, and Behavior, The Hebrew
University, Jerusalem, Israel. 5Natural Resources Institute,
University of Greenwich, Chatham, Kent, UK. 6Animal Flight
Laboratory, Department of Evolutionary and Environmental
Biology, University of Haifa, Haifa, Israel.
*Corresponding author. Email: firstname.lastname@example.org (G.H.);
email@example.com (J. W.C.)