Order Chiroptera is one of the most diverse of the orders of the animal kingdom.
The smallest bat weighs only about 1.5 g and has a wingspan of about 10 cm, whereas the largest species weighs about 1.5 kg and has a wingspan of about 1.7 m.
Bats are found in almost all habitats, on all continents (except Antarctica), and constitute about one fifth of all mammal species. Among the characteristics unique to the order, the most notable are the highly developed flight, recognized as one of the main factors in their success, and the use of echolocation - a sense whose operation is similar to that of radar, which will be discussed further below.
The definition of the order Chiroptera has undergone very significant updates recently, and therefore there are gaps between the sources available to us. In most of them, the order Chiroptera is presented as divided into two suborders:
1. "megabats" - Megachiroptera 
2. "microbats" - Microchiroptera
The basis of this division is the assumption that insectivorous bats and fruit bats share a common ancestor, but genetic findings indicate otherwise. Before turning to the currently accepted division, it should be noted that although in Hebrew it is customary to call the large ones "fruit bats" and the small ones "insectivorous bats", in fact fruit and insects are not a clear characteristic of the diet of species from these groups. The Egyptian fruit bat (Rousettus aegyptiacus) is the only representative in the country of the suborder of the large bats. It is indeed considerably larger and heavier than all the insectivorous bats in the country (more than 30 species in Israel), but in fact there are "large bats" in the world (fruit bats) that are smaller than "small bats" (insectivorous bats).
Doubts regarding the common origin of "large" bats and "small" bats began to arise back in the 1980s: a surprising morphological closeness was discovered between representatives of the two suborders, and over the years genetic findings placed fruit bats alongside insectivorous bats.
Today, a new division of the order Chiroptera is agreed upon in a different way, but even regarding it opinions are divided and more information is needed in order to establish it.
Vespertilioniformes (Yangochiroptera) - which includes most of the insectivorous bat families known from the traditional classification.
Yinpterochiroptera) Pteropodiformes) - a suborder that includes 4 insectivorous bat families and the fruit bat family.
Adopting the new division has far-reaching implications (!) 
The existence of a common ancestor with flight ability makes it possible to draw a relatively simple path of development and degeneration of various traits and abilities in the areas of flight and echolocation. In contrast, the new division requires that flight evolved independently in the Megachiroptera, that echolocation evolved twice, and more. 
The Egyptian fruit bat (fruit bat) is unusual among fruit bats in that it uses echolocation, which may indicate its development; below are references to two sources dealing with this. The third source is among the most important on the subject of the new division of the order Chiroptera. In the bibliographies of these articles one can find references to many additional sources:
Pettigrew JD, Maseko BC, Manger PR (April 2008). "Primate-like retinotectal decussation in an echolocating megabat, Rousettus aegyptiacus". Neuroscience 153 (1): 226–31
Holland, Richard A. et al. (Dec 2004). "Echolocation signal structure in the Megachiropteran bat Rousettus aegyptiacus Geoffroy 1810". J Exp Biol 207 (25): 4361–4369
Teeling, E.C.; Springer, M. S.; Madsen, O.; Bates, P.; O'Brien, S. J.; Murphy, W. J. (2005). "A Molecular Phylogeny for Bats Illuminates Biogeography and the Fossil Record". Science 307 (5709): 580–584
In Israel there are 33 bat species, which make up about one third of all mammal species in the country. Except for one species - the Egyptian fruit bat, which feeds on fruit - the rest of the species belong to what was formerly called the "suborder of small bats". They feed on insects and therefore are of great benefit to humans - they are the main predator of species of moths harmful to agriculture. Fruit bats, in tropical areas, are also very significant in the context of pollination and seed dispersal of plants.
 

מתי והיכן ניתן לצפות בעטלפים?
Entry into caves in which insectivorous bats hibernate is prohibited during the winter season. The reason is that insectivorous bats feed on insects, and most insects are less active in winter, when the air temperature drops. Insectivorous bats store a little fat in autumn, and feed on it during the long winter, when they greatly reduce their activity. In order for the food reserve to suffice for the bats for the entire winter period, they reduce their metabolism relative to the normal consumption during periods when the bat is active. In this state: a. The heart rate drops sharply. b. The body temperature drops from 40 degrees (in flight) to a temperature close to the cave temperature.
Entering a cave in which bats are hibernating causes the bats to awaken and causes the burning of much of the fat they need in order to "get through" the winter safely. After the bats "wake up" due to entry into the cave, the bats remain with much less fat, and some will be left with too few food reserves, making it difficult for them to survive the winter season!!

Bats can be observed in all parts of the country, and there are species active throughout the year, even in the heart of the big cities. They are relatively easy to spot above bodies of water and can be seen hunting insects around street lamps, which also provide lighting for observation. Fruit bats that are attracted to fruit trees (for example, chinaberry) can be observed - because of their size, many details can be distinguished even without any aid equipment.

Most species in Israel are endangered, why?
The fruit bat used to be considered a pest — back then, fruit was picked relatively late in the ripening stage, when it was still attractive as food for fruit bats (in the 1960s, harvesting methods changed). In attempts to eradicate fruit bats — smoking caves with a substance now known to be carcinogenic, within nature reserves, with the active assistance of conservation bodies and illegally, as a court later ruled — entire populations of insectivorous bats were destroyed. The slow reproduction rate of insectivorous bats did not allow them to recover, even after cave smoking was stopped. Most species, and as mentioned bats constitute about a third of all mammal species in Israel, are endangered. The pale serotine, according to the Red Book, is already extinct. More information in the article The distress of the fruit bat. 

How, then, can bats be observed?
Bats can be observed while they are active — it is possible to locate a fruit tree that attracts fruit bats and watch them without any equipment from a distance of a few meters. Because of their size, many details can be seen without any observation equipment. With binoculars, many more details can be discerned, and we may even be able to observe a female fruit bat carrying a pup. Insectivorous bats can be observed hunting in flight above water sources and around street lamps. If a bat colony is known to us, we can position ourselves near it in the evening and watch them against the bright sky as they emerge for activity. 
What equipment is needed?
Bats can also be observed without using any special equipment at all; however, in order to identify and become familiar with bats, one must be equipped with a detector, an essential tool for observing bats just as binoculars are essential for observing birds. 

What is a detector needed for?
Echolocation (echo location / bio-sonar) 

 In his book Bats, gives B. Fenton a brief historical overview of the developments in the field, based on which the introduction above was written. The book is highly recommended as a first guide, easy and pleasant to read, and includes wonderful photographs — some of them were even taken in Israel. 
Everyone in the field from the authority, from the Society for the Protection of Nature, and from academia, has joined forces to establish the site - writing, correcting, updating, and adding information - and for that we all give thanks. 
Many thanks toEyal Bartov, Afi First andRonit Orbaum whose photographs are displayed on the site