Hot, dry weather is the single biggest reason grasshoppers seem to be everywhere at once. Grasshoppers thrive when warm temperatures speed up their development and drought weakens the fungal diseases that normally keep their numbers in check. If your yard, garden, or hiking trail suddenly feels overrun, the conditions that favor you being outdoors in summer also happen to favor explosive grasshopper reproduction. But the story is more interesting than just “it’s been warm lately,” because climate patterns, land use, and even the grasshoppers’ own brain chemistry all play roles in whether you see a handful or a horde.
Warm, Dry Conditions Are the Main Trigger
Grasshoppers are cold-blooded, so their metabolism, growth rate, and reproductive timing all accelerate as temperatures rise. A stretch of warm weather in spring and early summer means eggs hatch sooner, nymphs develop faster, and adults appear in greater numbers within a compressed window of time. That compressed timing is why it can feel like they all showed up overnight: many individuals in a region are hitting adulthood at roughly the same moment.
Drought compounds the effect. When rainfall drops, the fungal pathogens that normally thin grasshopper populations struggle to survive. One of the most important of these is Entomophaga grylli, a naturally occurring fungus that infects and kills grasshoppers in the wild. Research on this pathogen in intermountain grasslands found that when moisture was experimentally increased, fungal spore levels jumped eightfold and the survival time of infected grasshoppers was cut in half.1The Canadian Entomologist. Abiotic effects on the clear-winged grasshopper (Orthoptera: Acridae) and its fungal pathogen Entomophaga grylli (Entomophthorales: Entomophthoraceae) in an intermountain bunch-grass prairie In other words, a wet year is bad news for grasshoppers because their biggest natural disease runs rampant. A dry year flips that equation: the fungus can’t reproduce well, and grasshopper populations balloon.
So the combination of warmth plus drought is what turns a normal grasshopper season into an overwhelming one. If you’ve had a mild winter followed by a dry spring and hot summer, that’s the recipe. Two or three such years in a row can produce truly spectacular numbers, because each generation starts from a larger egg bank than the year before.
Climate Change Is Reshuffling Where and When They Appear
If grasshoppers seem more common than they were a decade ago, there may be a longer-term explanation layered on top of any single year’s weather. Warming temperatures are shifting the geographic ranges of many grasshopper species northward and pushing their seasonal emergence earlier in the year. Modeling of six common North American grasshopper species found that early-season species showed northern range expansions of roughly 20 to 80 percent more suitable habitat area during spring months under warming scenarios. Species whose ranges once topped out around Iowa and Nebraska were projected to find suitable conditions as far north as the Dakotas and Montana.2PubMed Central. Phenology dictates the impact of climate change on geographic distributions of six co‐occurring North American grasshoppers
That range expansion means people in areas that historically didn’t see many grasshoppers are now encountering them more frequently. If you live in the northern Great Plains, the Upper Midwest, or the northern Rockies, the grasshoppers that arrive each summer may include species whose ancestors stayed farther south a few decades ago.
Warmer conditions also appear to make individual grasshoppers bigger. Research examining grasshopper body size across elevations and seasons found that grasshoppers tend to capitalize on warmth by both growing larger and reaching adulthood earlier.3PLOS Biology. Insect size responses to climate change vary across elevations according to seasonal timing Bigger grasshoppers are simply more noticeable. A half-inch nymph hiding in the grass barely registers; a two-inch adult launching itself across a sidewalk is hard to miss. If warming trends are producing both more individuals and larger individuals, the visual impression of “grasshoppers everywhere” has a real biological basis.
Grasshoppers Versus Locusts and the Swarming Question
When grasshoppers seem unusually abundant, a common worry is whether you’re seeing something closer to a locust swarm. Locusts are actually grasshoppers, specifically certain species that can switch between a solitary phase and a gregarious, swarming phase. Most of the grasshoppers you see in a North American backyard are species that don’t undergo this dramatic behavioral switch. They can still be extremely numerous, but they aren’t forming coordinated swarms the way desert locusts or migratory locusts do.
The phase-change mechanism in true locusts is fascinating in its own right. Research on migratory locusts has shown that the neurotransmitter serotonin plays a key role in maintaining solitary behavior. When gregarious locust nymphs were isolated, serotonin levels in their brains rose, and pharmacological experiments showed that boosting serotonin in already-isolating locusts accelerated the shift toward solitary behavior. Conversely, activating a specific serotonin receptor pathway during crowding actually inhibited the switch to gregarious behavior.4PubMed Central. Serotonin enhances solitariness in phase transition of the migratory locust The implication is that for true locusts, whether the animals become destructive swarmers or stay as harmless loners is partly a matter of brain chemistry responding to crowding cues.
For the common grasshoppers blanketing a suburban lawn, this phase-change biology doesn’t apply. But high-density populations of ordinary grasshopper species can still cause plenty of damage to gardens and crops even without the coordinated movement of a locust swarm. The practical effect on your tomato plants may look similar either way.
What Normally Keeps Grasshopper Numbers in Check
In a typical year, grasshopper populations are held down by a web of natural controls. Fungal pathogens like Entomophaga grylli are among the most effective, as described earlier, but they depend heavily on moist conditions. When rain is adequate, the fungus can cause localized die-offs that dramatically thin grasshopper numbers before they reach pest levels.
Beyond disease, grasshoppers face a long list of predators. Birds are the most visible ones: meadowlarks, killdeer, hawks, and even chickens readily eat grasshoppers. Spiders, ground beetles, robber flies, and blister beetle larvae also prey on various grasshopper life stages. Parasitic flies and wasps lay eggs inside grasshoppers, and their larvae consume the host from within. Small mammals such as shrews and mice eat grasshoppers opportunistically.
Cold winters kill off eggs that were deposited in shallow or exposed soil, so a particularly harsh winter can reduce the following summer’s population. Conversely, mild winters leave more eggs viable, contributing to the boom you see the next year. Late-spring freezes after eggs have hatched can also wipe out early nymphs, but the timing has to be just right.
When drought removes the pathogen pressure and a mild winter removes the cold-kill pressure simultaneously, the remaining predators often can’t compensate. That’s when populations explode. It usually takes a return to normal or above-average rainfall, which boosts fungal disease and plant growth (giving predators more cover to hunt from), to bring numbers back down over one or two seasons.
What All Those Grasshoppers Are Doing to Your Ecosystem
Grasshoppers are among the most abundant insects in grassland ecosystems worldwide, and they do more than eat your garden. They are a critical link in nutrient cycling and the food web, serving as a major food source for arthropods, birds, and mammals.5Basic and Applied Ecology. Grasshoppers affect grassland ecosystem functioning: Spatial and temporal variation Every grasshopper that gets eaten transfers plant energy up the food chain. In areas with healthy grasshopper populations, the birds and small predators that depend on them are also healthier.
Their herbivory has a less obvious but equally important effect on the soil. A five-year experiment found that grasshoppers speed up nitrogen cycling by changing the amount and decomposition rate of plant litter. The net result was an increase in total plant abundance of up to about 18 percent.6PubMed Central. Insect herbivory accelerates nutrient cycling and increases plant production Grasshoppers eat selectively, often targeting certain plant species over others, and their droppings return nitrogen to the soil in a form that plants can use more quickly than undigested leaf litter. Over time, this selective feeding and rapid nutrient return can shift which plant species dominate a landscape, generally favoring plants that are better at competing when nitrogen is more available.
This means a grasshopper boom isn’t purely destructive from an ecological standpoint. In native grasslands, periodic high-density years are part of the natural cycle. The damage becomes a problem mainly in agricultural settings or ornamental gardens, where the plants being eaten are ones we’ve chosen and cultivated rather than wild species that have evolved alongside grasshopper pressure.
Why Some Plants Survive and Others Get Devoured
If you’ve noticed that grasshoppers annihilate some plants in your garden while ignoring others, that selectivity is well documented. Grasshoppers generally prefer grasses and broadleaf plants with high nutrient content and low levels of defensive chemicals. Plants that produce bitter or toxic secondary compounds are less palatable and less nutritious for grasshoppers. Research on the grasshopper Oedaleus asiaticus found that individuals fed plants rich in secondary compounds grew more slowly and had reduced digestive enzyme activity compared to those fed on nutritious grasses.7PubMed Central. Biology, physiology and gene expression of grasshopper Oedaleus asiaticus exposed to diet stress from plant secondary compounds The grasshoppers could survive on the chemically defended plants, but they had to ramp up detoxification processes and paid a growth penalty for it.
This has practical implications for anyone trying to protect a garden during a boom year. Plants in the mint family, marigolds, and other strongly aromatic or bitter-tasting species tend to be lower on the grasshopper menu. Vegetables like lettuce, corn, and beans are highly preferred. Tall, lush grasses are almost irresistible. If you’re designing a landscape in an area prone to grasshopper outbreaks, mixing in plants with strong chemical defenses can reduce the overall damage, though nothing is entirely grasshopper-proof when populations are at their peak.
Physical barriers like floating row covers remain the most reliable garden protection during outbreaks. Insecticidal baits containing Nosema locustae, a protozoan pathogen specific to grasshoppers, can help if applied early in the season when nymphs are small, but they work slowly and are less effective against large adult populations. Broad-spectrum insecticides kill grasshoppers on contact but also destroy the predatory insects that help control them, potentially making the next year worse.
The Rocky Mountain Locust and a Cautionary Tale
It’s worth remembering that North America once had a grasshopper problem that dwarfs anything modern observers have seen. The Rocky Mountain locust, Melanoplus spretus, formed swarms so massive in the 1870s that one documented cloud of insects was estimated to cover an area larger than California. Settlers on the Great Plains reported skies darkened for days and crops stripped to bare soil in hours.
Then, within roughly three decades, the species went completely extinct. The currently accepted explanation is habitat destruction: the conversion of montane river valleys to agriculture in the late 1800s eliminated the specific breeding habitat the species depended on.8Terrestrial Arthropod Reviews. The fate of the Rocky Mountain locust, Melanoplus spretus Walsh: implications for conservation biology Farmers unknowingly plowed up the very river-valley soils where the locust laid its eggs, and the population collapsed from billions to zero in a geological instant.
The Rocky Mountain locust story cuts both ways for thinking about modern grasshopper booms. On one hand, it shows that grasshopper outbreaks are not new, and the scale of historical events makes current yard invasions look modest. On the other hand, it illustrates how dependent grasshopper populations are on specific habitat conditions. The same landscape changes that accidentally exterminated one species have created favorable conditions for others, particularly species that thrive in agricultural fields and suburban lawns rather than undisturbed prairie.
When to Expect Numbers to Drop
If you’re in the middle of a grasshopper-heavy summer, the most reliable predictor of relief is rain. A wet late summer and fall promote fungal disease in adult grasshoppers and reduce the number of eggs that successfully overwinter. A wet spring the following year keeps pathogen pressure high on the emerging nymphs. Two consecutive seasons of above-average moisture will usually bring even a serious outbreak back to normal levels.
A harsh winter with deep, sustained freezing temperatures also helps, particularly if snow cover is thin. Snow actually insulates egg pods in the soil, so a cold winter with heavy snow can paradoxically protect eggs better than a slightly warmer but snowless one. The worst-case scenario for grasshopper control is a dry fall, a mild winter with little snow, and another dry spring: that sequence lets the maximum number of eggs survive and hatch into conditions where their natural enemies are weakened.
Individual grasshopper adults don’t live long. Most species complete their life cycle in a single season, with adults dying off by mid-autumn in temperate regions. The grasshoppers you’re seeing now will be gone within weeks of the first hard frost. Whether their offspring return in force next year depends almost entirely on the moisture and temperature conditions between now and next June. If the forecast calls for a wet autumn and a cold winter, you can expect a much quieter grasshopper season when summer comes around again.