The Economist April 2nd 2022 Science & technology 73divert a missile by interfering with its
guidance systems—for instance, by daz
zling them with infrared light or lasers.
Hardkill systems are intended to destroy
missiles in flight.
The war in Ukraine shows the limita
tions of the softkill approach, says Jack
Watling of the Royal United Services Insti
tute, a thinktank in London. “You need a
good technical understanding of the sys
tem you’re trying to defeat.” The potpourri
of atgms fielded by Ukrainian soldiers
comes with many different guidance sys
tems. Jamming all of them is impossible.
But hardkill systems have problems,
too. You need sophisticated radar to detect
incoming missiles, and precise aim to hit
them. Antitank missiles travel at hun
dreds of metres a second, so quick reaction
times are vital.
The Soviet Drozd system, one of the
first hardkill apss, was initially deployed
in the 1980s, in the wake of the ussr’s inva
sion of Afghanistan. It fired shells full of
shotgunlike pellets at incoming missiles.
Afghanit, Drozd’s most recent successor, is
built into Russia’s brandnew t14 tanks.
But Russia has struggled to construct
enough of these. As best as analysts can
tell, few apsequipped tanks have so far
been sent into Ukraine.
The army that is furthest along with
hardkill apss is Israel’s. Its Trophy system
is designed by Rafael, a firm in Haifa, and is
fitted to the country’s Merkava tanks. Tro
phy fires a tight spread of precisely aimed
projectiles, the idea being to minimise the
danger the system poses to nearby friendly
infantry. Israel’s army claims that Trophy
has defeated many antitank rocket attacks
in Gaza—though Mr Hawkes notes that
such attacks are probably from older, less
sophisticated atgms. Trophy has attracted
interest from abroad, too. America and
Germany have equipped some tanks with it
and Britain is running trials.
There are downsides to such defences.
apss take up weight, space and power—all
precious commodities in a tank. Western
tanks, in particular, says Mr Watling, have
little room to grow heavier without com
promising performance. And hardkill sys
tems may protect against only a handful of
incoming rounds, since debris from a suc
cessful interception is likely to damage the
delicate radar on which the system relies.
Crafty enemies could rake tanks with
machinegun fire to disable this radar be
fore the fact, says Mr Watling.
But a defence does not have to be per
fect to be useful. Mr Hawkes talks of multi
layered, “onionstyle” defences, in which
screening infantry spot threats, smoke can
obscure a tank’s location, and armour then
protects the target if all else fails. Russia’s
experienceinUkraine suggests adding an
other layertothat onion could prove use
ful indeed.n
E
arthworms’benignimageasaer
ators, drainers and fertilisers of field
and garden belies a darker secret. They
are actually fierce competitors with other
invertebrates, voraciously consuming
rotting plant matter and tiny organisms
such as protists, nematodes, bacteria and
fungi, all of which might otherwise
sustain a wide variety of soil dwellers.
That much is well known, not least
from research conducted in northern
North America. Here, worms were wiped
out during the last ice age, which ended
12,000 years ago. They started returning,
in the form of European interlopers, only
a few centuries in the past. What have
not been investigated much until now
are the consequences of this subterra
nean carnage for surfacedwelling crit
ters. But that has just been corrected by
Malte Jochum of Leipzig University, in
Germany, and his colleagues, in a study
just published in Biology Letters.
Dr Jochum and his team worked in a
forest overlooking Barrier Lake, in Alber
ta, Canada, where the earthworm in
vasion has been tracked for three de
cades. That has permitted the identifica
tion of areas with low (four worms per
square metre, on average), medium (43
worms per square metre) and high (106
per square metre) populations.
Within each zone of abundance the
researchers marked 20 plots with indi
vidual areas of two square metres. They
identified all of the plants therein and
used vacuumsuction collecting devices
to “hoover” up as many as possible of the
abovesurface arthropods (mostly in
sects and spiders) in each plot. They then
sorted, identified and measured these
animals to calculate their abundance,biomassandspeciesrichness.
Altogether, the collectors picked up
13,037 individual arthropods—and dis
crepancies between plots were quickly
obvious. Those with abundant earth
worms were depauperised of arthropods
compared with ones where worms were
rare. Plots with the most worms in them
had 61% fewer individual arthropods,
18% fewer arthropod species and a 27%
diminution in total arthropod biomass,
compared with those with the fewest.
Socalled detritivores—which com
pete directly with worms for food—
suffered worst. There were 80% less of
them in areas of worm abundance, com
pared with those of worm scarcity. But
herbivores and omnivores suffered, too.
Only for carnivorous arthropods, such as
spiders, was there good news. Their
numbers were up 41% in wormrich
plots, compared with wormpoor ones.
Why predators did well is unclear.
Some, perhaps, were eating worms di
rectly. Others may have taken advantage
of the stripping of cover for their prey
caused by worms pulling the leaflitter
underground for later consumption.
The knockon effects of this carnage
further up the food chain, among in
vertebrateeating amphibians, reptiles,
birds and mammals, remain obscure.
Species that like to consume worms are
presumably doing better, while those
that prefer their meals crunchy, rather
than squishy, will be doing worse.
Whether this matters in the grand
scheme of things is debatable. But for
those who prefer their ecosystems pris
tine, this work confirms that earthworms
are certainly not the unalloyed good
which some people make them out to be.InvasivespeciesNews from the underground
Worms are changing North America’s ecology