Heat Packs Cold Packs

Heat packs and cold packs play a surprisingly important role in the breeding side of invertebrate keeping. Anytime you are moving breeding stock between locations, sending offspring to new homes, or dealing with a sudden temperature swing in your animal room, these simple tools can mean the difference between healthy arrivals and dead-on-arrival losses. If you breed invertebrates with any intention of selling or trading offspring, understanding how these packs work is something you need to sort out before your first shipment goes out the door.

This topic applies to essentially every invertebrate group kept in captivity. Tarantula breeders shipping slings in winter need heat packs. Isopod keepers mailing cultures during summer heat waves need cold packs. Even if you never ship a single animal, a power outage in January or a broken air conditioner in August can put your entire breeding colony at risk, and having the right packs on hand gives you options when things go sideways.

Getting temperature management right matters because invertebrates cannot regulate their own body temperature. They are completely at the mercy of their environment, and during shipping or emergencies, that environment is whatever you create inside a box or enclosure. Eggs and young offspring are especially vulnerable because they have less body mass and fewer reserves to survive temperature extremes. A gravid female exposed to freezing temperatures during transit may drop her egg sac. A culture of tropical isopods left in a hot delivery truck without a cold pack can be wiped out completely.

New breeders often ask whether these packs are really necessary or just an extra expense. They wonder how long packs actually last and how to position them inside a shipping box without cooking or freezing the animals they are trying to protect. The details matter more than people expect. A heat pack placed directly against a deli cup will kill a sling just as surely as the cold it was meant to prevent.

This article covers the types of heat and cold packs available to invertebrate breeders, how they work, when you need them, and how to use them properly in shipping and emergency situations. You will learn how to match pack duration to transit time, insulate and position packs safely, and what species-specific considerations affect your choices.

Heat packs used in the invertebrate hobby are almost always the same iron-powder-based hand warmers sold in sporting goods stores. When exposed to air, the iron powder oxidizes and produces heat. Standard 40-hour heat packs maintain temperatures between 100 and 130 degrees Fahrenheit at the surface, which is far too hot for direct contact with any invertebrate. The key principle is that heat packs warm the air inside an insulated box, not the animal directly. You are creating a warm microclimate, and insulation is what makes the whole system work.

Cold packs for invertebrate shipping come in two main varieties. Phase-change cold packs contain a gel that absorbs heat as it melts from a frozen state, keeping the box interior cooler than outside temperatures. Evaporative cold packs use moisture and airflow to reduce temperatures. For most invertebrate shipping, frozen gel packs wrapped in newspaper are the standard choice. They do not get as cold as dry ice, making them safer for live animals, and provide a gradual cooling effect that lasts through typical transit windows.

The biology behind this is simple. Invertebrates are ectotherms, meaning their body temperature matches their surroundings. When air temperature drops below their tolerance range, metabolism slows dramatically and cellular damage begins. For tropical species, temperatures below 50 degrees Fahrenheit can cause irreversible damage within hours. Heat stress is equally dangerous, with sustained temperatures above species-specific thresholds causing rapid dehydration and organ failure. Eggs in incubation are even less tolerant because developing embryos have no behavioral options for coping. They cannot burrow deeper or seek shade. Whatever temperature you expose them to is what they experience.

Using heat packs in practice means thinking about pack duration, insulation thickness, and positioning. For overnight shipping within 18 to 24 hours, a standard 40-hour pack provides enough coverage. For two-day transit, you may need a 72-hour pack. The pack should be taped to the box lid or interior wall, separated from animal containers by at least one inch of insulation such as crumpled newspaper or foam sheeting. Never place a heat pack directly against any container holding a live animal.

Cold pack usage follows similar logic in reverse. Freeze the gel pack solid, wrap it in several layers of newspaper to prevent condensation dripping onto animal containers, and position it with adequate separation. Cold packs lose effectiveness faster than heat packs, so shipping windows need to be tighter during extreme summer heat. Many breeders avoid shipping when destination temperatures exceed 100 degrees because even good cold pack systems cannot overcome a box sitting on a metal delivery truck in direct sun.

The ethical dimension connects directly to your responsibility as a breeder. When you sell and ship a living animal, you are responsible for its welfare until it reaches the buyer. Cutting corners on insulation or skipping packs to save a few dollars is not acceptable when a life depends on your packaging. If weather conditions make safe shipping impossible, the responsible choice is to hold the shipment until conditions improve.

Tarantula and scorpion breeders are probably the most experienced group when it comes to heat pack usage because the sling and juvenile trade has been shipping animals through the mail for decades. Tarantula slings are typically packed in small vials or deli cups with damp paper towel, placed inside an insulated box with a heat pack during cold months. The important arachnid-specific consideration is that both tarantulas and scorpions are sensitive to overheating, so the insulation barrier between heat pack and animal containers needs to be generous. A sling can survive brief exposure to 50-degree air, but sustained exposure to 110-degree air from a poorly positioned heat pack will kill it outright.

Insect breeders face different challenges depending on species. Mantis oothecae shipped to buyers need protection from cold but are relatively tolerant compared to live nymphs because the egg case provides some insulation. Live mantis nymphs, stick insect nymphs, and beetle larvae are more vulnerable and need careful heat pack positioning. Roach colonies being shipped are somewhat hardier, but tropical species like death's head roaches still need heat packs when overnight lows drop below 45 degrees along the shipping route. Cold packs matter for insects during summer because many species cannot tolerate sustained temperatures above 95 degrees.

Myriapod breeders shipping millipedes or centipedes deal with an additional factor, which is moisture retention. Millipedes need humid conditions during transit, and heat packs can dry out box air surprisingly fast. Experienced millipede breeders use slightly damp sphagnum moss inside the animal container and add extra insulation to buffer against the drying effect. Centipedes are more tolerant of brief temperature dips than most tropical millipedes but are also more likely to injure themselves if they become overly active from heat pack warmth in a small container.

Crustacean and mollusk breeders face the most complex challenges because many species are aquatic or semi-aquatic. Shipping live shrimp or crayfish involves insulated boxes, breather bags, and temperature management that accounts for water temperature rather than just air. Water changes temperature more slowly than air, providing some buffer, but once water gets too cold or hot it stays that way longer. Isopod breeders shipping terrestrial cultures use the same general approach as insect breeders. Snail breeders pack animals in damp moss, positioning heat packs well away because snails are particularly sensitive to dehydration from warm dry air.

Across all groups, the universal principle is that you need to know your species' temperature tolerance range before choosing pack type, duration, and placement. A desert scorpion has very different cold tolerance than a tropical tarantula. A temperate millipede handles cooler temperatures better than a tropical giant African species. Research your specific animals and never assume what works for one species translates directly to another.

Before your first shipment goes out, build yourself a shipping station with everything you need in one place. Stock up on 40-hour and 72-hour heat packs, gel cold packs that fit your standard box size, insulated shipping boxes or styrofoam liners, packing materials like crumpled newspaper and foam sheets, and tape. Buy heat packs in bulk from reptile or invertebrate supply vendors rather than paying retail for individual hand warmers, because the cost difference adds up fast when you are shipping regularly. Keep a few cold packs in your freezer at all times so they are ready when you need them.

When you are packing a shipment, activate your heat pack at least 20 minutes before sealing the box so it reaches operating temperature and you can confirm it is working. Tape it to the inside of the box lid with the air-facing side pointing inward. Place a layer of crumpled newspaper or foam between the pack and the animal containers, making sure there is at least an inch of separation everywhere. Position the animal containers in the center of the box, surrounded by insulation on all sides. For cold pack shipments, wrap the frozen pack in three or four layers of newspaper to prevent condensation from dripping, and position it the same way you would a heat pack, with insulation separating it from the animals.

Monitoring your results is essential for improving your shipping success rate over time. Ask every buyer to report arrival condition, including whether animals were active or sluggish, whether containers were wet from condensation, and what the temperature was at their location when the box arrived. Keep a simple log with the date, destination, weather conditions, pack type used, and arrival report. After a dozen shipments you will have a clear picture of what works and what needs adjustment for different seasons and destinations.

When things go wrong, the most common problems are heat packs that fail to activate, cold packs that thaw too quickly, and transit delays that exceed your pack duration. If a buyer reports dead-on-arrival animals that appear heat-damaged, you probably positioned the pack too close or used insufficient insulation. If animals arrive cold and sluggish, the pack may have expired or your insulation was inadequate for the transit time and outside temperature. Adjust accordingly for your next shipment. Some breeders include a temperature indicator strip inside the box so the buyer can report what the peak and low temperatures were during transit.

Responsible breeders plan shipments around weather forecasts and avoid shipping when conditions at origin, destination, or anywhere along the route present extreme temperatures. Most breeders follow a general rule of not shipping when any point along the route will experience temperatures below 35 or above 95 degrees Fahrenheit. This means accepting that there will be weeks or even months when shipping is not safe, and communicating that clearly to buyers who may not understand why their order is delayed. Building this expectation into your sales process from the beginning prevents frustration on both sides.

The most common mistake breeders make with heat packs is placing them directly against animal containers without adequate insulation. It seems logical that closer means warmer, but a 40-hour heat pack running at 120 degrees pressed against a thin plastic deli cup creates a lethal hot zone that will cook whatever is inside. This kills more shipped invertebrates than cold weather does, which is ironic given that the pack was meant to protect them. Always maintain separation, always insulate between the pack and the animals, and always test your setup with a thermometer before you trust it with live cargo.

Another frequent error is failing to account for the full transit time including delays. A 40-hour heat pack sounds like plenty for overnight shipping, but overnight shipping does not always mean 18 hours door to door. Weather delays, sorting facility backlogs, and missed connections can push delivery to 36 or even 48 hours. If your heat pack expires at hour 40 and the box sits in a cold warehouse for another eight hours, the temperature inside drops rapidly. Experienced breeders use longer-duration packs than they think they need and ship early in the week to avoid weekend warehouse holds where nobody is moving packages.

Neglecting to check weather conditions along the entire shipping route, not just at origin and destination, catches many breeders off guard. You might be shipping from a mild 65-degree location to another mild 60-degree location, but if the package routes through a sorting facility in Minnesota where it is 10 below zero, the interior of that box is going to plummet regardless of what the weather is doing at either end. Check the route, check the forecast at hub cities, and make conservative decisions.

Some breeders skip temperature management altogether for species they consider hardy, assuming that a roach colony or a batch of isopods can handle whatever transit throws at them. This works until it does not. Even hardy species have limits, and a box sitting on a frozen loading dock or inside a sun-baked delivery truck exceeds those limits faster than people expect. The animals that survive rough shipping may appear fine but carry stress damage that shows up days later as die-offs or failed breeding attempts. Stress removal equals cooperation, and that starts with making transit as gentle as possible.

The ethical failure behind all these mistakes is treating shipping as an afterthought rather than a core responsibility of the breeding operation. If you are producing offspring for sale, the obligation to get them to buyers alive and healthy is not optional. Building proper shipping supplies and protocols into your operation from the start, pricing your animals to cover those costs, and refusing to ship when conditions are unsafe demonstrates the kind of professionalism the hobby needs more of. Every dead-on-arrival package damages buyer trust and reflects poorly on the entire invertebrate breeding community.

Heat packs and cold packs are fundamental tools for any invertebrate breeder who ships animals or manages a breeding room where temperature emergencies can occur. They are inexpensive, widely available, and effective when used correctly. The core principles are straightforward: insulate between packs and animals, match pack duration to transit time with a safety margin, position packs so they warm or cool the air rather than contacting containers directly, and test your setups before trusting them with live animals. Having supplies on hand before you need them means you are never scrambling when a cold snap hits or a buyer is ready for their order.

Your responsibility as a breeder extends to every moment between when an animal leaves your care and when it arrives safely at its destination. Cutting corners on temperature management to save a few dollars or a few minutes of packing time is not acceptable when living creatures are involved. Build shipping costs into your pricing, stock supplies before you need them, and treat every shipment as if the animal inside is one you care about personally, because your buyer certainly does. The breeders who earn lasting reputations in this hobby are the ones whose animals consistently arrive alive and healthy.

Species-specific research matters enormously here because temperature tolerances vary widely across invertebrate groups. What works for a desert scorpion does not work for a tropical millipede. What protects a tarantula sling in winter may be unnecessary for a temperate isopod culture. Know your species, know their limits, and pack accordingly. When in doubt, add more insulation rather than less, and use a longer-duration pack rather than hoping a shorter one will be enough.

Getting this right is one of those practical skills that separates breeders who build a solid reputation from those who burn through buyers with repeated shipping losses. The investment is small, the learning curve is manageable, and the payoff is animals arriving alive, healthy, and ready to thrive in their new homes. That is the outcome every responsible breeder should be working toward with every package they send.