Most bumble bee species are not invasive. They are native pollinators that play essential roles in their home ecosystems. But a handful of species, moved around the world by the commercial greenhouse industry, have escaped into environments where they don’t belong and are now causing serious ecological damage. The most problematic of these is the large earth bumble bee, Bombus terrestris, which has established invasive populations on nearly every continent outside its native range.
Why Bumble Bees Were Shipped Worldwide
The story starts in 1985, when a Belgian veterinarian discovered that bumble bees could pollinate greenhouse tomatoes far more efficiently than human workers, who had previously shaken each plant by hand three times a week. Bumble bees are better suited to indoor pollination than honey bees because of their smaller colonies, shorter foraging ranges, and a vibration technique called buzz pollination that releases pollen from tomato flowers. Three companies quickly scaled up commercial production, and roughly 95% of their bumble bee colonies go to tomato greenhouses. By 2010, the industry was shipping over 140,000 commercial colonies per year to growers worldwide.
The problem is containment. Greenhouses are not sealed environments. Queens and males escape, mate outdoors, and establish feral populations. Once a species gets a foothold, it spreads on its own.
Which Species Have Become Invasive
Ten bumble bee species have been recorded establishing populations outside their native ranges. Four are particularly widespread:
- Bombus terrestris (large earth bumble bee): Native to Europe, North Africa, and western Asia. Now invasive in New Zealand, Japan, South Korea, Chile, Argentina, Tasmania, and Iceland.
- Bombus impatiens (common eastern bumble bee): Native to eastern North America. Has spread into western North America, Mexico, and Central America through commercial use.
- Bombus ruderatus: Native to Europe. Established in New Zealand, Chile, Argentina, and the Canary Islands.
- Bombus subterraneus: Native to Europe. Established in New Zealand.
Bombus terrestris is the most commercially traded species and the most aggressively invasive. Its global expansion began in the 1880s, when it was first shipped to New Zealand for clover pollination. The real boom came a century later with industrial-scale rearing in the 1980s, and it hasn’t slowed since.
How Invasive Bumble Bees Harm Native Species
Direct Competition for Food
Invasive bumble bees compete with native pollinators for nectar and pollen, and they have a trick that gives them an unfair advantage. When flower tubes are too deep for their tongues, they bite holes near the base to steal nectar directly, a behavior called nectar robbing. Research in raspberry fields across Patagonia found that flowers from robbed buds contained half the nectar and produced only two-thirds as much nectar as unrobbed flowers. The proportion of robbed buds increased with bumble bee abundance, meaning higher invasive populations leave less food for every other pollinator in the area, including managed honey bees.
Reproductive Interference
In Japan, escaped Bombus terrestris queens and males from greenhouses in Hokkaido have established feral populations that are driving two native species into decline. One mechanism is particularly insidious: invasive males mate with native queens, but the resulting eggs never develop. Native queens that mate with B. terrestris males produce no viable offspring. Researchers on the Nemuro Peninsula found that about 4.4% of native B. hypocrita sapporensis queens had stored sperm from B. terrestris males. Those queens are reproductive dead ends, wasting an entire season without producing a colony.
Disease Spillover
Commercial bumble bee hives carry gut parasites at alarming rates. A study of commercially reared B. terrestris hives imported into Ireland found that 60% were infected with the microsporidian Nosema bombi and 35% carried Crithidia, an intestinal parasite. These pathogens don’t stay in the greenhouse. Researchers detected elevated parasite levels in wild bumble bee populations up to 2 kilometers from greenhouses using commercial hives.
The consequences for wild bees are severe. Crithidia bombi reduces lifetime reproductive output of queens by 40% when infection occurs before hibernation and increases worker mortality by 50% during food-scarce periods. Nosema bombi can deform wings, kill workers and males, and prevent queens from mating. In North America, rapidly declining bumble bee species consistently show higher prevalence of N. bombi compared to stable species. In Japan, tracheal mites originally from European rearing facilities have crossed into native populations, confirmed through DNA analysis showing European mite lineages now present in wild Japanese bees.
South America: A Case Study in Rapid Spread
Chile imported Bombus terrestris for greenhouse pollination starting in the late 1990s. The species quickly escaped and established feral populations. Argentina, which banned B. terrestris imports, was invaded anyway through spillover from Chile. Researchers compiled 562 occurrence records from 2000 to 2019 and found that the invaded area has expanded at a constant, linear rate with no sign of slowing. The data fits a linear model with over 94% accuracy, suggesting the invasion is still in its expansion phase and will likely reach other South American countries.
This expansion has been devastating for native pollinators. Bombus dahlbomii, the largest native bumble bee in South America, has experienced dramatic population declines in areas where B. terrestris has arrived. The invasive species also disrupts relationships between native plants and their pollinators, a cascade that affects plant reproduction across entire ecosystems.
Australia’s Containment Effort
Bombus terrestris became established in Tasmania, likely arriving sometime in the 1990s, but so far has not reached the Australian mainland. Victoria treats bumble bees as a priority biosecurity threat. A single dead bee was found in inner Melbourne in March 2020, prompting follow-up surveillance that found no additional specimens. Australia has no native bumble bees at all, which means an invasion of the mainland could be especially destructive since native plants and pollinators have no evolutionary history with bumble bees.
Why Regulation Has Failed
On paper, safeguards exist. Chile, for example, has required since 1997 that imported bumble bee shipments be certified free of specific pathogens, including tracheal mites and the fat-tissue parasite Apicystis bombi. In practice, these measures have not worked. Analysis of the international trade found that neither exporting nor importing countries established effective sanitary measures to manage the risks. Commercial colonies continued to arrive carrying the very pathogens they were supposed to be screened for.
The scale of the industry makes enforcement difficult. Tens of thousands of colonies cross international borders each year, the greenhouse tomato industry alone was valued at over $10 billion globally in 2021, and the economic pressure to keep shipping bees is enormous. Some regions have responded with outright bans. Argentina prohibited B. terrestris imports but couldn’t stop the species from crossing the border on its own. The tension between agricultural productivity and ecological protection remains unresolved in most countries where commercial bumble bees are used.
Native Bumble Bees Are a Different Story
If you’re watching a bumble bee visit flowers in your garden in North America, Europe, or Asia, it is almost certainly a native species doing exactly what it evolved to do. North America alone has around 50 native bumble bee species, and only about 1% of all bee species on the continent are non-native. The invasion problem is specific to a few commercially traded species that have been deliberately moved outside their natural ranges. Native bumble bees are not pests. Many are in decline themselves, threatened by habitat loss, pesticide exposure, climate change, and the very diseases spread by their commercially shipped relatives.