It is usually husbands who crack the jokes about difficult, interfering mothers-in-law.

But their wives probably have more reason to complain.

A study of hundreds of families has found that mothers are far more likely to feud with a daughter-in-law than a son-in-law.

Nearly two-thirds of daughters-in-law accused their husband's mother of 'unreasonably jealous maternal love'.

A similar proportion of mothers-in-law complained they had been isolated and excluded by a female addition to the family.

Dr Terri Apter, a psychologist at Newnham College, Cambridge, has spent 20 years researching the type of battles seen in the film Monster-in-Law, starring Jane Fonda and Jennifer Lopez.

She interviewed 49 couples and 156 other people, and drew on past studies to compile her new book, What Do You Want From Me?

She said: 'As they struggle to achieve the same position in the family as primary woman, each tries to establish or protect their status, each feels threatened by the other.

'Mother-in-law and daughter-in-law conflict often emerges from an expectation that each is criticizing or undermining the other. But this mutual unease may have less to do with actual attitudes and far more to do with persistent female norms that few of us manage to shake off completely.'

These 'norms' include the fact that wives are still usually in charge of the cooking, cleaning and children's welfare - opening them up to criticism from an older woman who has done it all before.

And many women cannot break the habits of childhood, when they ousted rivals from playground cliques using subtle and indirect insults over extended periods of time. Dr Apter said one woman she spoke to began receiving messages from her mother-in-law-to-be two months before the wedding.

Jenny, 26, from North London, said one warned: 'My son thinks about me every day, every minute of the day, every second of every minute of the day.' Other letters were critical, intrusive or seeking pity.

Another interviewee, mother-in-law Annie, 64, from Yorkshire, said: 'My daughter-in-law is so cold towards me.

'She begrudges any time or attention my son gives to me and takes every opportunity to minimise the importance and depth of bond he and I have.'

女婿们常爱拿难缠多事的丈母娘开开玩笑。

而媳妇们可能有更多抱怨的理由。

一项针对数百个家庭的调查发现，婆媳关系比岳母和女婿的关系难处得多。

调查显示，近三分之二的儿媳称她们的婆婆“溺爱儿子，常常吃醋”。

另有相同比例的婆婆则抱怨由于儿媳的出现，她们被冷落了。

英国剑桥大学纽汉姆学院的心理学家特里?阿普特博士在过去20年中对婆媳冲突的类型进行了研究，由影星简?芳达和詹妮佛?洛佩兹主演的电影《怪兽婆婆》就讲述了婆媳之间针锋相对的故事。

为编写新书《想从我这里得到什么？》，特里博士对49对夫妇和另外156人进行了访问，并借鉴了之前的一些研究成果。

她说：“婆婆和儿媳都争当家庭中的女主人，她们都试图建立和维护自己在家庭中的地位，双方都感觉受到了对方的威胁。”

“婆媳冲突的原因通常是双方都认为对方在指责或贬低自己。但这种互相看不惯与实际态度无关，而与我们都无法完全摆脱的“女性常规”紧密相连。

这些“常规”包括媳妇在家庭中仍负责做饭、打扫房间和照顾孩子等家务事，而在这些方面经验丰富的婆婆难免会批评她们。

而且很多女性无法改掉儿时的习惯，女孩小时候通常会与对手长期地暗地里较劲以将她们挤出自己的小圈子。阿普特博士称，一位受访女性称，她在结婚前两个月就不断地收到婆婆的来信。

来自伦敦北部的26岁的珍妮称，她的婆婆在一封信中“警告”她说：“我的儿子每天、每分钟、每秒钟都在想我。”其他的信要么是指责叨扰，要么是寻求同情。

而另一位受访者、来自约克郡的64岁的婆婆安妮说：“儿媳对我的态度十分冷漠。”

她说：“只要儿子和我在一起，或者关心我，她就不乐意。她还利用一切机会疏远我和儿子的关系。”