What heat, cold, and a little extra travel time mean for a very small predator.
A predatory mite can spend its life on a leaf, where conditions change between morning and afternoon, shade and sun, one day and the next. The temperature that helps it reproduce fastest is not the only temperature it can survive.
That distinction can get lost when the mite is in a shipping box. Suddenly, a warm afternoon, a cold night, or an overnight depot stop can look like the end of the entire population. But leaving ideal conditions does not automatically kill a mite. An extra day in transit does not come with a biological off switch.
To understand what happens during shipping, we need to follow the conditions around the mites: how hot or cold they become, how long that lasts, and whether they have the moisture and resources to get through it. Those pieces work together.
Comfortable and survivable are different things
A species’ preferred temperature range usually describes conditions that support feeding, development, and reproduction. That is useful information when choosing predators for a plant, where we want them to hunt and, ideally, establish a population.
Outside that range, those activities do not all stop at once. Development may slow or egg production may fall while adults remain alive. Conditions can be unsuitable for raising the next generation without being immediately lethal to the current one.
Shipping asks the mites to get through a temporary change. Establishing asks them to keep feeding and reproducing over time. Confusing those two tasks makes a preferred temperature range look much more like a survival limit than it really is.
A hot afternoon is part of a temperature history
Consider a day that heats up in the afternoon and cools overnight. The hottest reading tells us the peak, but it leaves out all the hours spent below it. A mite experiencing that cycle has a different exposure from one held continuously at the peak temperature.
In a heat-wave experiment with persimilis, most reached adulthood under a daily cycle peaking at about 100°F and cooling overnight. They had prey, moist leaf arenas, and shelter. The hotter cycle changed their development and adult size, but survival remained high.1
Heat still has limits. In another experiment, persimilis exposed to four-hour periods at 97–104°F could continue developing and reproducing afterward, although survival and reproduction were affected. Eggs exposed for four hours at about 108°F did not hatch.2 The useful lesson is the relationship between intensity and time: surviving a hot interval does not mean tolerating the same heat indefinitely.
For a shipment, that temperature history belongs to the mites inside their container. The outdoor forecast helps describe the route, but the packaging and surrounding conditions determine how closely the temperature inside follows it.
Cold slows the pace
Cooling can have a very different effect. At suitable cool temperatures, mites’ biological activity slows. Researchers use this response to extend storage: a temperature too low for rapid population growth can still preserve life.
In a humidity-controlled storage study, adult female californicus survived an average of 11 weeks at about 46°F. Persimilis averaged eight weeks at 41°F.3 These were carefully maintained conditions, including saturated water vapor, rather than an ordinary refrigerator. Even so, the finding makes the distinction clear. Cool and dead are not interchangeable.
Mites can also respond to a change before it becomes severe. In a californicus experiment, an hour at 41°F before a much colder exposure substantially improved survival compared with going straight into the severe cold. This response is called rapid cold hardening.4 Recent conditions can influence how well a mite handles the next change.
Temperature alone, however, does not explain the long survival in the storage study. The researchers also kept the mites from drying out. That brings us to a part of shipping that receives much less attention than the weather forecast.
Moisture and food help mites wait
A mite needs both enough moisture to avoid drying out and enough resources to sustain itself. Keeping one of those needs covered does not make the other disappear.
In a californicus study, researchers held adult females in small vials with a leaf disk, predator eggs as food, or both. The leaf disk increased humidity. Females given both food and the humid environment survived much longer than those given either alone.5
This helps explain why elapsed time tells only part of the shipping story. A day with supportive conditions is a different challenge from a day spent drying out without food. The environment inside the container influences how long the mites can wait.
It also explains why adding something to warm or cool a box deserves more thought than simply matching the opposite of the forecast. Temperature changes affect moisture conditions, too.
Do predatory mites need an ice pack?
An ice pack can provide a temporary buffer against warming. It absorbs heat as it melts, so arriving melted does not mean it failed to do anything. Melting is part of the job.7 How much cooling reaches the mites depends on the pack, the packaging, and the surrounding temperatures.
We include ice packs, but they are not intended to keep the mites refrigerator-cold for the whole trip. A still-cold pack is reassuring to find when opening a box; it is not a requirement for the mites to arrive alive.
Cooling also changes relative humidity—the amount of water vapor in the air compared with what it could hold at that temperature. With the same amount of water vapor, cooler air has higher relative humidity. Water vapor can also condense into droplets on the cold pack’s surface.8, 9 That familiar dampness comes from moisture already in the air.
The pack therefore influences the environment around it, but its condition at delivery cannot tell us the temperature or humidity the mites experienced inside their bottle or sachet throughout the trip.
Heat packs bring a drying tradeoff
Warming brings the opposite moisture tradeoff. When air warms without gaining water vapor, its relative humidity falls.8 A box can become warmer and drier in relative terms at the same time.
For predatory mites, that can work against the goal of preserving life. The cold-storage research shows that suitable cool, humid conditions can sustain them for substantial periods; adding warmth without maintaining moisture can increase the challenge of drying out.3, 5 This is why we do not include heat packs with predatory mites.
The packing decision is about the combination of conditions around the mites. A cold forecast alone does not establish a need for supplemental heat, just as a warm forecast does not mean the package must remain cold from departure to arrival.
Wholesale and retail are different scales
That environment also helps explain why packing advice for an order of millions of mites may not describe an order of 500. The species has the same biological needs at either scale, but the containers, carrier material, concentration of mites, and outer packaging can differ.
A large order may contain multiple separate containers. A small consumer order still has carrier material around its predators. Neither the total mite count nor a photograph of another shipment tells us how a particular bottle is packed or what conditions develop inside it.
When applying the research to a shipment, the useful questions concern that actual environment: temperature, moisture, resources, and time. Wholesale packaging is one example of meeting those needs, rather than a standard against which every retail box should be judged.
Depots, delivery trucks, and an extra night
The package’s surroundings change during the journey as well. A UPS or FedEx parcel moves through collection, sorting facilities, transport between facilities, and final delivery. The van that arrives at the house handles the last leg. UPS’s “out for delivery” status marks dispatch from the local facility to the driver.6
Time at a depot and time on a delivery route are different exposures. A temperature reported from one vehicle cannot describe the entire journey, and the outdoor high is not a temperature record for the mites inside the box. The route includes different settings and both warmer and cooler hours.
An overnight stop or a weekend delay extends that journey. It does not, by itself, tell us that conditions became lethal. The mites continue responding to their surroundings: supportive conditions allow them to wait longer, while prolonged stress uses up more of their margin.
Prompt delivery preserves that margin. An extra day is still additional time, but it is not evidence on its own that the mites have died.
Arrival changes the task
Once the mites reach the plant, surviving the journey gives way to finding prey and continuing to feed. Establishing a population asks more of them still: adults need to reproduce, eggs need to hatch, and the young need to survive.
This is where preferred conditions become especially useful. In the heat studies, some effects appeared in development and reproduction; in the cold-storage study, persimilis could survive prolonged storage but lay fewer eggs afterward.1, 2, 3 Being alive and building a population are connected, but they are different measures of success.
A mite can tolerate a temporary change on the way to your home and still need suitable conditions once it gets there. The journey is a short part of its life. The plant is where it has to make a living.
Sources and research notes
The biological studies below examine temperature tolerance, development, and storage under controlled conditions. We use them to explain survival during transit, rather than predict the outcome of a particular delivery. Packing observations are drawn from our practice; the additional references explain delivery stages and the physics of temperature and moisture.
- Tscholl and colleagues (2022). Heat waves affect prey and predators differently via developmental plasticity: who may benefit most from global warming? Pest Management Science, 78, 1099–1108. Extreme regime: daily chamber temperatures 22–38°C (72–100°F); prey, moist leaf arenas, and refuges provided.
- Effects of Short-Term Heat Stress on the Development, Reproduction, and Demographic Parameters of Phytoseiulus persimilis (2025). Insects, 16, 596. Eggs were exposed for four hours; mites reaching adulthood received a further four-hour exposure. Other rearing was at 25°C. This is not evidence for continuous multi-day survival at the treatment temperatures.
- Ghazy and colleagues (2014). Air temperature optimisation for humidity-controlled cold storage of Neoseiulus californicus and Phytoseiulus persimilis. Pest Management Science. Mated adult females; saturated water vapor. Reported durations are mean survival times, not guarantees for every individual.
- Rapid cold hardening response in the predatory mite Neoseiulus californicus (2014). Direct exposure to −10°C (14°F) for two hours left no more than 2% of adult females alive; prior acclimation at 5°C (41°F) for one hour raised survival to 75%. The comparison demonstrates how prior acclimation changes cold tolerance.
- Ghazy & Amano (2016). The use of the cannibalistic habit and elevated relative humidity to improve the storage and shipment of Neoseiulus californicus. Experimental and Applied Acarology, 69, 277–287. Individually held adult females at 25°C; experimental food and humidity treatments, not courier performance data.
- UPS. Understanding Tracking Status. Describes network transit and dispatch from the local facility for final delivery.
- OpenStax. Phase Change and Latent Heat. Explains the absorption of heat during melting; does not quantify cooling in a mite shipment.
- National Weather Service. Humidity. Explains how relative humidity changes with temperature when the amount of water vapor remains constant.
- U.S. Geological Survey. Condensation and the Water Cycle. Explains the conversion of water vapor to liquid droplets on cool surfaces.
