question: how do bugs and insects keep coming back after the winter?
comment: There's a bunch of different ways. Some critters, like frogs, have high levels of glucose in their blood, which acts like a natural anti freeze. They also burrow to avoid the harsh elements. Insects can produce alcohols that essentially does the same thing. Bees will huddle together in the hive and buzz together to keep their body heat up. But many insects do actually die during winter, leaving behind eggs that can survive the elements and hatch in the spring.
passages: Cold temperatures outside will cause invasions beginning in the late summer months and early fall. Box elder bugs, cluster flies, ladybugs, and silverfish are noticed some of the most common insects to seek the warm indoors.
  
  Section::::Modern techniques.
   The lifespan of the "Blissus leucopterus" is a typically less than one year. The eggs of two generations are laid down from spring to summer, when they develop into adults. During the fall, the adults from the first generation die off, while the adults from the second generation retreat from the crops to look for overwinter shelters. The adults overwinter in any type of shelters they can find, including in hedgerows, road sides, bushy fence rows, edges of woodlands, and soybean stubble, under tree barks and bunch grass, and inside field mice nests. Once they emerge from their hibernation, they return to the crop fields to feast and breed before their death.
   Section::::Aquatic insects.
   BULLET::::- March – April: Daytime temperature stays above 20 °C for a few hours. The Blissus leucopterus emerge from hibernation and begin mating.
  
  BULLET::::- April – May: The adults fly to fields with small grains growing (such as wheat) and start sucking the sap out of them. They continue to mate while the females begin laying eggs on the lower leaves of plants, or on the roots. They will continue to do so for the next 30 days, laying a total of around 200 eggs.
   The adults mostly overwinter in leaf litter in woods but some find refuge among rough vegetation. When the temperature reaches about they seek out cereal crops, start to feed on the stems, leaves and developing seed heads, mate and lay their eggs. There is only one generation each year so adults and nymphs can be found feeding together on the ripening grain. If the insects are not fully developed when the crop is harvested, some nymphs and young adults feed and mature on fallen grain and other crop residues before flying off to their winter quarters. In Syria, they spend about nine months in hibernation.
   Another common winter migrant insect, found in much of North America, South America, and the Caribbean, is the Green Darner. Migration patterns in this species are much less studied than those of monarchs. Green darners leave their northern ranges in September and migrate south. Studies have noted a seasonal influx of green darners to southern Florida, which indicates migratory behavior. Little has been done with tracking of the green darner, and reasons for migration are not fully understood since there are both resident and migrant populations. The common cue for migration southward in this species is the onset of winter.
   Section::::Freeze avoidance.
   Section::::Freeze tolerance.
   Section::::Freeze tolerance.:Ice nucleators.
  
  In order for a body of water to freeze, a nucleus must be present upon which an ice crystal can begin to grow. At low temperatures, nuclei may arise spontaneously from clusters of slow-moving water molecules. Alternatively, substances that facilitate the aggregation of water molecules can increase the probability that they will reach the critical size necessary for ice formation.
   During certain times of the year boxelder bugs cluster together in large groups while sunning themselves on warm surfaces near their host tree (e.g. on rocks, shrubs, trees, and man-made structures). This is especially a problem in the fall when they are seeking a warm place to overwinter. Large numbers are often seen congregating on houses seeking an entry point. Once they have gained access, they remain inactive behind siding and inside of walls while the weather is cool. Once the home's heating system becomes active for the season, the insects may falsely perceive it to be springtime and enter inhabited parts of the home in search of food and water. Once inside inhabited areas of a home, their excreta may stain upholstery, carpets, drapes, and they may feed on certain types of house plants. In the spring, the bugs leave their winter hibernation locations to feed and lay eggs on maple or ash trees. Clustered masses of boxelder bugs may be seen again at this time, and depending on the temperature, throughout the summer. Their outdoor congregation habits and indoor excreta deposits are perceived as a nuisance by many people, therefore boxelder bugs are often considered pests. However, boxelder bugs are harmless to people and pets. The removal of boxelder trees and maple trees can help control boxelder bug populations. Spiders are minor predators, but because of the boxelder bug's chemical defenses few birds or other animals will eat them. Boxelder bug populations are not affected by any major diseases or parasites.
   "Chelifer cancroides" is the species most commonly found in homes, where they are often observed in rooms with dusty books. There the tiny animals () can find their food like booklice and house dust mites. They enter homes by "riding along" attached to insects (known as phoresy). The insects employed are necessarily larger than the pseudoscorpion, or they are brought in with firewood.
  
  Section::::Evolution.
   The graphs show seasonal occurrence for one species only i.e. "Ixodes holocyclus". The extent to which other species found in the area parallel "Ixodes holocyclus" in this and other aspects of their biology is not known.
  
  The graphs show the average seasonal prevalence of instars and types, observed over an eight-year period, which includes six years of detailed field observation, and collection, supported by information and specimens from many people.
   Coccinellids in temperate regions enter diapause during the winter, so they often are among the first insects to appear in the spring. Some species (e.g., "Hippodamia convergens") gather into groups and move to higher elevations, such as a mountain, to enter diapause.
  
  Most coccinellids overwinter as adults, aggregating on the south sides of large objects such as trees or houses during the winter months, dispersing in response to increasing day length in the spring.
   Section::::Impact of climate change on agriculture.:Pest insects and climate change.
  
  Global warming could lead to an increase in pest insect populations, harming yields of staple crops like wheat, soybeans, and corn. While warmer temperatures create longer growing seasons, and faster growth rates for plants, it also increases the metabolic rate and number of breeding cycles of insect populations. Insects that previously had only two breeding cycles per year could gain an additional cycle if warm growing seasons extend, causing a population boom. Temperate places and higher latitudes are more likely to experience a dramatic change in insect populations.
   Section::::Survival strategies.
  
  Two major strategies for winter survival have evolved in the Class Insecta due to their inability to generate significant heat metabolically. The first, migration, is a complete avoidance of the temperatures that pose a threat. If an insect cannot migrate, then it must stay and deal with the cold temperatures in one of two ways. This cold hardiness is separated into two categories, freeze avoidance and freeze tolerance.
  
  Section::::Migration.
  
  See: Insect migration
   Changes have already been observed in the distribution of insects active year-round. As an example, during the past thirty years, the Sachem Skipper butterfly of California extended its northernmost edge north into WA State. We can expect to see many more examples of such changes in range or distribution in the future.
   A number of migratory contractors, known as "custom harvesters", move with their combines to follow the wheat harvest in the United States and Canada. as the season moves north. Some crop dusters are also migratory, following seasonal patterns of need. In the large citrus districts of Florida and California seasonal pickers arrive for collection periods and often move with the changing harvest.
   Pehr Kalm, a Swedish naturalist visiting Pennsylvania and New Jersey in 1749 on behalf of his nation's government, observed in late May an emergence of Brood X. When reporting the event in a paper that a Swedish academic journal published in 1756, Kalm wrote: The general opinion is that these insects appear in these fantastic numbers in every seventeenth year. Meanwhile, except for an occasional one which may appear in the summer, they remain underground.brThere is considerable evidence that these insects appear every seventeenth year in Pennsylvania.
   BULLET::::3. Re-allocation of energy within the body associated with the movement
   Some species of Collembola tolerate extreme cold by the shedding of the mid-gut during moulting.
   Other insect species may benefit from warmer temperatures. Increased voltinism and winter survival in many insects has the potential for dramatic population increases in pest species such as foliage-eating Lepidoptera and bark-boring Coleoptera.
   Freeze avoidance involves both physiological and biochemical mechanisms. One method of freeze avoidance is the selection of a dry hibernation site in which no ice nucleation from an external source can occur. Insects may also have a physical barrier such as a wax-coated cuticle that provides protection against external ice across the cuticle. The stage of development at which an insect over-winters varies across species, but can occur at any point of the life cycle (i.e., egg, pupa, larva, and adult).
   In the home, products susceptible to infection should be kept in sealed containers to exclude these beetles. Freezing infested foodstuffs at -18 °C for six days will kill all stages of the O. mercator life cycle. Infestations always center around a food source used for breeding and the identification and removal of all infested foodstuffs will eliminate the population
   The next step in the development of these biological agents is to determine at what stage in the pests' life cycle fungi could best be used. Two possibilities are
  
  BULLET::::1. As they migrate to the fields in the early spring
  
  BULLET::::2. In their over wintering sites among the foothills surrounding the fields.
   This mayfly may have a shorter life cycle than other members of its genus. In the laboratory when kept at a warm temperature it has been reared from egg to adulthood in thirteen weeks, but in the Keokuk area there is believed to be a single generation per year, whereas in Kentucky Lake there is mixed voltinism, with some adults emerging at 14 months and others at 22 months.
  
  Section::::Human impact.
  
  Sometimes "H. bilineata" adults emerge simultaneously in vast numbers. On July 14, 1958, The Des Moines Register reported that the previous evening:
  